diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 40050890..31eb3c45 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -82,6 +82,10 @@ jobs:
             os: ubuntu-latest
             python-version: '3.10'
             tox-env: gmpy2py310
+          - name: py3.11
+            os: ubuntu-latest
+            python-version: '3.11.0-alpha.3'
+            tox-env: py311
           - name: pypy
             os: ubuntu-latest
             python-version: pypy-2.7
diff --git a/src/ecdsa/__init__.py b/src/ecdsa/__init__.py
index 4eb4e6a3..ce8749aa 100644
--- a/src/ecdsa/__init__.py
+++ b/src/ecdsa/__init__.py
@@ -37,13 +37,9 @@
     InvalidSharedSecretError,
 )
 from .der import UnexpectedDER
+from . import _version
 
 # This code comes from http://github.com/tlsfuzzer/python-ecdsa
-from ._version import get_versions
-
-__version__ = get_versions()["version"]
-del get_versions
-
 __all__ = [
     "curves",
     "der",
@@ -90,3 +86,5 @@
     six.b(""),
 ]
 del _hush_pyflakes
+
+__version__ = _version.get_versions()["version"]
diff --git a/src/ecdsa/_version.py b/src/ecdsa/_version.py
index 2a12077f..8c4354fd 100644
--- a/src/ecdsa/_version.py
+++ b/src/ecdsa/_version.py
@@ -5,7 +5,7 @@
 # that just contains the computed version number.
 
 # This file is released into the public domain. Generated by
-# versioneer-0.17 (https://github.com/warner/python-versioneer)
+# versioneer-0.21 (https://github.com/python-versioneer/python-versioneer)
 
 """Git implementation of _version.py."""
 
@@ -56,7 +56,7 @@ class NotThisMethod(Exception):
 
 
 def register_vcs_handler(vcs, method):  # decorator
-    """Decorator to mark a method as the handler for a particular VCS."""
+    """Create decorator to mark a method as the handler of a VCS."""
 
     def decorate(f):
         """Store f in HANDLERS[vcs][method]."""
@@ -73,20 +73,20 @@ def run_command(
 ):
     """Call the given command(s)."""
     assert isinstance(commands, list)
-    p = None
-    for c in commands:
+    process = None
+    for command in commands:
         try:
-            dispcmd = str([c] + args)
+            dispcmd = str([command] + args)
             # remember shell=False, so use git.cmd on windows, not just git
-            p = subprocess.Popen(
-                [c] + args,
+            process = subprocess.Popen(
+                [command] + args,
                 cwd=cwd,
                 env=env,
                 stdout=subprocess.PIPE,
                 stderr=(subprocess.PIPE if hide_stderr else None),
             )
             break
-        except EnvironmentError:
+        except OSError:
             e = sys.exc_info()[1]
             if e.errno == errno.ENOENT:
                 continue
@@ -98,15 +98,15 @@ def run_command(
         if verbose:
             print("unable to find command, tried %s" % (commands,))
         return None, None
-    stdout = p.communicate()[0].strip()
+    stdout = process.communicate()[0].strip()
     if sys.version_info[0] >= 3:
         stdout = stdout.decode()
-    if p.returncode != 0:
+    if process.returncode != 0:
         if verbose:
             print("unable to run %s (error)" % dispcmd)
             print("stdout was %s" % stdout)
-        return None, p.returncode
-    return stdout, p.returncode
+        return None, process.returncode
+    return stdout, process.returncode
 
 
 def versions_from_parentdir(parentdir_prefix, root, verbose):
@@ -118,7 +118,7 @@ def versions_from_parentdir(parentdir_prefix, root, verbose):
     """
     rootdirs = []
 
-    for i in range(3):
+    for _ in range(3):
         dirname = os.path.basename(root)
         if dirname.startswith(parentdir_prefix):
             return {
@@ -128,9 +128,8 @@ def versions_from_parentdir(parentdir_prefix, root, verbose):
                 "error": None,
                 "date": None,
             }
-        else:
-            rootdirs.append(root)
-            root = os.path.dirname(root)  # up a level
+        rootdirs.append(root)
+        root = os.path.dirname(root)  # up a level
 
     if verbose:
         print(
@@ -149,22 +148,21 @@ def git_get_keywords(versionfile_abs):
     # _version.py.
     keywords = {}
     try:
-        f = open(versionfile_abs, "r")
-        for line in f.readlines():
-            if line.strip().startswith("git_refnames ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["refnames"] = mo.group(1)
-            if line.strip().startswith("git_full ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["full"] = mo.group(1)
-            if line.strip().startswith("git_date ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["date"] = mo.group(1)
-        f.close()
-    except EnvironmentError:
+        with open(versionfile_abs, "r") as fobj:
+            for line in fobj:
+                if line.strip().startswith("git_refnames ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["refnames"] = mo.group(1)
+                if line.strip().startswith("git_full ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["full"] = mo.group(1)
+                if line.strip().startswith("git_date ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["date"] = mo.group(1)
+    except OSError:
         pass
     return keywords
 
@@ -172,10 +170,14 @@ def git_get_keywords(versionfile_abs):
 @register_vcs_handler("git", "keywords")
 def git_versions_from_keywords(keywords, tag_prefix, verbose):
     """Get version information from git keywords."""
-    if not keywords:
-        raise NotThisMethod("no keywords at all, weird")
+    if "refnames" not in keywords:
+        raise NotThisMethod("Short version file found")
     date = keywords.get("date")
     if date is not None:
+        # Use only the last line.  Previous lines may contain GPG signature
+        # information.
+        date = date.splitlines()[-1]
+
         # git-2.2.0 added "%cI", which expands to an ISO-8601 -compliant
         # datestamp. However we prefer "%ci" (which expands to an "ISO-8601
         # -like" string, which we must then edit to make compliant), because
@@ -188,11 +190,11 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         if verbose:
             print("keywords are unexpanded, not using")
         raise NotThisMethod("unexpanded keywords, not a git-archive tarball")
-    refs = set([r.strip() for r in refnames.strip("()").split(",")])
+    refs = set(r.strip() for r in refnames.strip("()").split(","))
     # starting in git-1.8.3, tags are listed as "tag: foo-1.0" instead of
     # just "foo-1.0". If we see a "tag: " prefix, prefer those.
     TAG = "tag: "
-    tags = set([r[len(TAG) :] for r in refs if r.startswith(TAG)])
+    tags = set(r[len(TAG) :] for r in refs if r.startswith(TAG))
     if not tags:
         # Either we're using git < 1.8.3, or there really are no tags. We use
         # a heuristic: assume all version tags have a digit. The old git %d
@@ -201,7 +203,7 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         # between branches and tags. By ignoring refnames without digits, we
         # filter out many common branch names like "release" and
         # "stabilization", as well as "HEAD" and "master".
-        tags = set([r for r in refs if re.search(r"\d", r)])
+        tags = set(r for r in refs if re.search(r"\d", r))
         if verbose:
             print("discarding '%s', no digits" % ",".join(refs - tags))
     if verbose:
@@ -210,6 +212,11 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         # sorting will prefer e.g. "2.0" over "2.0rc1"
         if ref.startswith(tag_prefix):
             r = ref[len(tag_prefix) :]
+            # Filter out refs that exactly match prefix or that don't start
+            # with a number once the prefix is stripped (mostly a concern
+            # when prefix is '')
+            if not re.match(r"\d", r):
+                continue
             if verbose:
                 print("picking %s" % r)
             return {
@@ -232,7 +239,7 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
 
 
 @register_vcs_handler("git", "pieces_from_vcs")
-def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
+def git_pieces_from_vcs(tag_prefix, root, verbose, runner=run_command):
     """Get version from 'git describe' in the root of the source tree.
 
     This only gets called if the git-archive 'subst' keywords were *not*
@@ -240,10 +247,12 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     version string, meaning we're inside a checked out source tree.
     """
     GITS = ["git"]
+    TAG_PREFIX_REGEX = "*"
     if sys.platform == "win32":
         GITS = ["git.cmd", "git.exe"]
+        TAG_PREFIX_REGEX = r"\*"
 
-    out, rc = run_command(
+    _, rc = runner(
         GITS, ["rev-parse", "--git-dir"], cwd=root, hide_stderr=True
     )
     if rc != 0:
@@ -253,7 +262,7 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
 
     # if there is a tag matching tag_prefix, this yields TAG-NUM-gHEX[-dirty]
     # if there isn't one, this yields HEX[-dirty] (no NUM)
-    describe_out, rc = run_command(
+    describe_out, rc = runner(
         GITS,
         [
             "describe",
@@ -262,7 +271,7 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
             "--always",
             "--long",
             "--match",
-            "%s*" % tag_prefix,
+            "%s%s" % (tag_prefix, TAG_PREFIX_REGEX),
         ],
         cwd=root,
     )
@@ -270,7 +279,7 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     if describe_out is None:
         raise NotThisMethod("'git describe' failed")
     describe_out = describe_out.strip()
-    full_out, rc = run_command(GITS, ["rev-parse", "HEAD"], cwd=root)
+    full_out, rc = runner(GITS, ["rev-parse", "HEAD"], cwd=root)
     if full_out is None:
         raise NotThisMethod("'git rev-parse' failed")
     full_out = full_out.strip()
@@ -280,6 +289,40 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     pieces["short"] = full_out[:7]  # maybe improved later
     pieces["error"] = None
 
+    branch_name, rc = runner(
+        GITS, ["rev-parse", "--abbrev-ref", "HEAD"], cwd=root
+    )
+    # --abbrev-ref was added in git-1.6.3
+    if rc != 0 or branch_name is None:
+        raise NotThisMethod("'git rev-parse --abbrev-ref' returned error")
+    branch_name = branch_name.strip()
+
+    if branch_name == "HEAD":
+        # If we aren't exactly on a branch, pick a branch which represents
+        # the current commit. If all else fails, we are on a branchless
+        # commit.
+        branches, rc = runner(GITS, ["branch", "--contains"], cwd=root)
+        # --contains was added in git-1.5.4
+        if rc != 0 or branches is None:
+            raise NotThisMethod("'git branch --contains' returned error")
+        branches = branches.split("\n")
+
+        # Remove the first line if we're running detached
+        if "(" in branches[0]:
+            branches.pop(0)
+
+        # Strip off the leading "* " from the list of branches.
+        branches = [branch[2:] for branch in branches]
+        if "master" in branches:
+            branch_name = "master"
+        elif not branches:
+            branch_name = None
+        else:
+            # Pick the first branch that is returned. Good or bad.
+            branch_name = branches[0]
+
+    pieces["branch"] = branch_name
+
     # parse describe_out. It will be like TAG-NUM-gHEX[-dirty] or HEX[-dirty]
     # TAG might have hyphens.
     git_describe = describe_out
@@ -324,15 +367,16 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     else:
         # HEX: no tags
         pieces["closest-tag"] = None
-        count_out, rc = run_command(
-            GITS, ["rev-list", "HEAD", "--count"], cwd=root
-        )
+        count_out, rc = runner(GITS, ["rev-list", "HEAD", "--count"], cwd=root)
         pieces["distance"] = int(count_out)  # total number of commits
 
     # commit date: see ISO-8601 comment in git_versions_from_keywords()
-    date = run_command(GITS, ["show", "-s", "--format=%ci", "HEAD"], cwd=root)[
+    date = runner(GITS, ["show", "-s", "--format=%ci", "HEAD"], cwd=root)[
         0
     ].strip()
+    # Use only the last line.  Previous lines may contain GPG signature
+    # information.
+    date = date.splitlines()[-1]
     pieces["date"] = date.strip().replace(" ", "T", 1).replace(" ", "", 1)
 
     return pieces
@@ -369,19 +413,71 @@ def render_pep440(pieces):
     return rendered
 
 
-def render_pep440_pre(pieces):
-    """TAG[.post.devDISTANCE] -- No -dirty.
+def render_pep440_branch(pieces):
+    """TAG[[.dev0]+DISTANCE.gHEX[.dirty]] .
+
+    The ".dev0" means not master branch. Note that .dev0 sorts backwards
+    (a feature branch will appear "older" than the master branch).
 
     Exceptions:
-    1: no tags. 0.post.devDISTANCE
+    1: no tags. 0[.dev0]+untagged.DISTANCE.gHEX[.dirty]
     """
     if pieces["closest-tag"]:
         rendered = pieces["closest-tag"]
+        if pieces["distance"] or pieces["dirty"]:
+            if pieces["branch"] != "master":
+                rendered += ".dev0"
+            rendered += plus_or_dot(pieces)
+            rendered += "%d.g%s" % (pieces["distance"], pieces["short"])
+            if pieces["dirty"]:
+                rendered += ".dirty"
+    else:
+        # exception #1
+        rendered = "0"
+        if pieces["branch"] != "master":
+            rendered += ".dev0"
+        rendered += "+untagged.%d.g%s" % (pieces["distance"], pieces["short"])
+        if pieces["dirty"]:
+            rendered += ".dirty"
+    return rendered
+
+
+def pep440_split_post(ver):
+    """Split pep440 version string at the post-release segment.
+
+    Returns the release segments before the post-release and the
+    post-release version number (or -1 if no post-release segment is present).
+    """
+    vc = str.split(ver, ".post")
+    return vc[0], int(vc[1] or 0) if len(vc) == 2 else None
+
+
+def render_pep440_pre(pieces):
+    """TAG[.postN.devDISTANCE] -- No -dirty.
+
+    Exceptions:
+    1: no tags. 0.post0.devDISTANCE
+    """
+    if pieces["closest-tag"]:
         if pieces["distance"]:
-            rendered += ".post.dev%d" % pieces["distance"]
+            # update the post release segment
+            tag_version, post_version = pep440_split_post(
+                pieces["closest-tag"]
+            )
+            rendered = tag_version
+            if post_version is not None:
+                rendered += ".post%d.dev%d" % (
+                    post_version + 1,
+                    pieces["distance"],
+                )
+            else:
+                rendered += ".post0.dev%d" % (pieces["distance"])
+        else:
+            # no commits, use the tag as the version
+            rendered = pieces["closest-tag"]
     else:
         # exception #1
-        rendered = "0.post.dev%d" % pieces["distance"]
+        rendered = "0.post0.dev%d" % pieces["distance"]
     return rendered
 
 
@@ -412,12 +508,41 @@ def render_pep440_post(pieces):
     return rendered
 
 
+def render_pep440_post_branch(pieces):
+    """TAG[.postDISTANCE[.dev0]+gHEX[.dirty]] .
+
+    The ".dev0" means not master branch.
+
+    Exceptions:
+    1: no tags. 0.postDISTANCE[.dev0]+gHEX[.dirty]
+    """
+    if pieces["closest-tag"]:
+        rendered = pieces["closest-tag"]
+        if pieces["distance"] or pieces["dirty"]:
+            rendered += ".post%d" % pieces["distance"]
+            if pieces["branch"] != "master":
+                rendered += ".dev0"
+            rendered += plus_or_dot(pieces)
+            rendered += "g%s" % pieces["short"]
+            if pieces["dirty"]:
+                rendered += ".dirty"
+    else:
+        # exception #1
+        rendered = "0.post%d" % pieces["distance"]
+        if pieces["branch"] != "master":
+            rendered += ".dev0"
+        rendered += "+g%s" % pieces["short"]
+        if pieces["dirty"]:
+            rendered += ".dirty"
+    return rendered
+
+
 def render_pep440_old(pieces):
     """TAG[.postDISTANCE[.dev0]] .
 
     The ".dev0" means dirty.
 
-    Eexceptions:
+    Exceptions:
     1: no tags. 0.postDISTANCE[.dev0]
     """
     if pieces["closest-tag"]:
@@ -490,10 +615,14 @@ def render(pieces, style):
 
     if style == "pep440":
         rendered = render_pep440(pieces)
+    elif style == "pep440-branch":
+        rendered = render_pep440_branch(pieces)
     elif style == "pep440-pre":
         rendered = render_pep440_pre(pieces)
     elif style == "pep440-post":
         rendered = render_pep440_post(pieces)
+    elif style == "pep440-post-branch":
+        rendered = render_pep440_post_branch(pieces)
     elif style == "pep440-old":
         rendered = render_pep440_old(pieces)
     elif style == "git-describe":
@@ -534,7 +663,7 @@ def get_versions():
         # versionfile_source is the relative path from the top of the source
         # tree (where the .git directory might live) to this file. Invert
         # this to find the root from __file__.
-        for i in cfg.versionfile_source.split("/"):
+        for _ in cfg.versionfile_source.split("/"):
             root = os.path.dirname(root)
     except NameError:
         return {
diff --git a/tox.ini b/tox.ini
index 7661d8cb..06079282 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 
 [tox]
-envlist = py26, py27, py33, py34, py35, py36, py37, py38, py39, py310, py, pypy, pypy3, gmpy2py27, gmpy2py39, gmpy2py310, gmpypy27, gmpypy39, gmpypy310, codechecks
+envlist = py26, py27, py33, py34, py35, py36, py37, py38, py39, py310, py311, py, pypy, pypy3, gmpy2py27, gmpy2py39, gmpy2py310, gmpypy27, gmpypy39, gmpypy310, codechecks
 
 [testenv]
 deps =
@@ -11,12 +11,12 @@ deps =
      py{26}: unittest2
      py{26}: hypothesis<3
      py{34}: attrs<21
-     py{26,27,34,35,36,37,38,39,310,py,py3}: pytest
-     py{27,34,35,36,37,38,39,310,py,py3}: hypothesis
-     gmpy2py{27,39,310}: gmpy2
-     gmpypy{27,39,310}: gmpy
-     gmpy{2py27,2py39,2py310,py27,py39,py310}: pytest
-     gmpy{2py27,2py39,2py310,py27,py39,py310}: hypothesis
+     py{26,27,34,35,36,37,38,39,310,311,py,py3}: pytest
+     py{27,34,35,36,37,38,39,310,311,py,py3}: hypothesis
+     gmpy2py{27,39,310,311}: gmpy2
+     gmpypy{27,39,310,311}: gmpy
+     gmpy{2py27,2py39,2py310,2py311,py27,py39,py310,py311}: pytest
+     gmpy{2py27,2py39,2py310,2py311,py27,py39,py310,py311}: hypothesis
 # six==1.9.0 comes from setup.py install_requires
      py27_old_six: six==1.9.0
      py27_old_six: pytest
@@ -53,6 +53,9 @@ basepython=python3.9
 [testenv:gmpypy310]
 basepython=python3.10
 
+[testenv:gmpypy311]
+basepython=python3.11
+
 [testenv:gmpy2py27]
 basepython=python2.7
 
@@ -62,6 +65,9 @@ basepython=python3.9
 [testenv:gmpy2py310]
 basepython=python3.10
 
+[testenv:gmpy2py311]
+basepython=python3.11
+
 [testenv:instrumental]
 basepython = python2.7
 deps =
diff --git a/versioneer.py b/versioneer.py
index fcdd1a36..81817f1f 100644
--- a/versioneer.py
+++ b/versioneer.py
@@ -1,4 +1,4 @@
-# Version: 0.17
+# Version: 0.21
 
 """The Versioneer - like a rocketeer, but for versions.
 
@@ -6,16 +6,12 @@
 ==============
 
 * like a rocketeer, but for versions!
-* https://github.com/warner/python-versioneer
+* https://github.com/python-versioneer/python-versioneer
 * Brian Warner
 * License: Public Domain
-* Compatible With: python2.6, 2.7, 3.2, 3.3, 3.4, 3.5, and pypy
-* [![Latest Version]
-(https://pypip.in/version/versioneer/badge.svg?style=flat)
-](https://pypi.python.org/pypi/versioneer/)
-* [![Build Status]
-(https://travis-ci.org/warner/python-versioneer.png?branch=master)
-](https://travis-ci.org/warner/python-versioneer)
+* Compatible with: Python 3.6, 3.7, 3.8, 3.9 and pypy3
+* [![Latest Version][pypi-image]][pypi-url]
+* [![Build Status][travis-image]][travis-url]
 
 This is a tool for managing a recorded version number in distutils-based
 python projects. The goal is to remove the tedious and error-prone "update
@@ -26,9 +22,10 @@
 
 ## Quick Install
 
-* `pip install versioneer` to somewhere to your $PATH
-* add a `[versioneer]` section to your setup.cfg (see below)
+* `pip install versioneer` to somewhere in your $PATH
+* add a `[versioneer]` section to your setup.cfg (see [Install](INSTALL.md))
 * run `versioneer install` in your source tree, commit the results
+* Verify version information with `python setup.py version`
 
 ## Version Identifiers
 
@@ -60,7 +57,7 @@
 for example `git describe --tags --dirty --always` reports things like
 "0.7-1-g574ab98-dirty" to indicate that the checkout is one revision past the
 0.7 tag, has a unique revision id of "574ab98", and is "dirty" (it has
-uncommitted changes.
+uncommitted changes).
 
 The version identifier is used for multiple purposes:
 
@@ -150,8 +147,8 @@
 software (exactly equal to a known tag), the identifier will only contain the
 stripped tag, e.g. "0.11".
 
-Other styles are available. See details.md in the Versioneer source tree for
-descriptions.
+Other styles are available. See [details.md](details.md) in the Versioneer
+source tree for descriptions.
 
 ## Debugging
 
@@ -165,7 +162,7 @@
 
 Some situations are known to cause problems for Versioneer. This details the
 most significant ones. More can be found on Github
-[issues page](https://github.com/warner/python-versioneer/issues).
+[issues page](https://github.com/python-versioneer/python-versioneer/issues).
 
 ### Subprojects
 
@@ -193,9 +190,9 @@
 Pip-8.1.1 is known to have this problem, but hopefully it will get fixed in
 some later version.
 
-[Bug #38](https://github.com/warner/python-versioneer/issues/38) is tracking
+[Bug #38](https://github.com/python-versioneer/python-versioneer/issues/38) is tracking
 this issue. The discussion in
-[PR #61](https://github.com/warner/python-versioneer/pull/61) describes the
+[PR #61](https://github.com/python-versioneer/python-versioneer/pull/61) describes the
 issue from the Versioneer side in more detail.
 [pip PR#3176](https://github.com/pypa/pip/pull/3176) and
 [pip PR#3615](https://github.com/pypa/pip/pull/3615) contain work to improve
@@ -223,22 +220,10 @@
 cause egg_info to be rebuilt (including `sdist`, `wheel`, and installing into
 a different virtualenv), so this can be surprising.
 
-[Bug #83](https://github.com/warner/python-versioneer/issues/83) describes
+[Bug #83](https://github.com/python-versioneer/python-versioneer/issues/83) describes
 this one, but upgrading to a newer version of setuptools should probably
 resolve it.
 
-### Unicode version strings
-
-While Versioneer works (and is continually tested) with both Python 2 and
-Python 3, it is not entirely consistent with bytes-vs-unicode distinctions.
-Newer releases probably generate unicode version strings on py2. It's not
-clear that this is wrong, but it may be surprising for applications when then
-write these strings to a network connection or include them in bytes-oriented
-APIs like cryptographic checksums.
-
-[Bug #71](https://github.com/warner/python-versioneer/issues/71) investigates
-this question.
-
 
 ## Updating Versioneer
 
@@ -264,6 +249,14 @@
 direction and include code from all supported VCS systems, reducing the
 number of intermediate scripts.
 
+## Similar projects
+
+* [setuptools_scm](https://github.com/pypa/setuptools_scm/) - a non-vendored build-time
+  dependency
+* [minver](https://github.com/jbweston/miniver) - a lightweight reimplementation of
+  versioneer
+* [versioningit](https://github.com/jwodder/versioningit) - a PEP 518-based setuptools
+  plugin
 
 ## License
 
@@ -273,7 +266,18 @@
 Dedication" license (CC0-1.0), as described in
 https://creativecommons.org/publicdomain/zero/1.0/ .
 
+[pypi-image]: https://img.shields.io/pypi/v/versioneer.svg
+[pypi-url]: https://pypi.python.org/pypi/versioneer/
+[travis-image]:
+https://img.shields.io/travis/com/python-versioneer/python-versioneer.svg
+[travis-url]: https://travis-ci.com/github/python-versioneer/python-versioneer
+
 """
+# pylint:disable=invalid-name,import-outside-toplevel,missing-function-docstring
+# pylint:disable=missing-class-docstring,too-many-branches,too-many-statements
+# pylint:disable=raise-missing-from,too-many-lines,too-many-locals,import-error
+# pylint:disable=too-few-public-methods,redefined-outer-name,consider-using-with
+# pylint:disable=attribute-defined-outside-init,too-many-arguments
 
 from __future__ import print_function
 
@@ -323,13 +327,13 @@ def get_root():
         # module-import table will cache the first one. So we can't use
         # os.path.dirname(__file__), as that will find whichever
         # versioneer.py was first imported, even in later projects.
-        me = os.path.realpath(os.path.abspath(__file__))
-        me_dir = os.path.normcase(os.path.splitext(me)[0])
+        my_path = os.path.realpath(os.path.abspath(__file__))
+        me_dir = os.path.normcase(os.path.splitext(my_path)[0])
         vsr_dir = os.path.normcase(os.path.splitext(versioneer_py)[0])
         if me_dir != vsr_dir:
             print(
                 "Warning: build in %s is using versioneer.py from %s"
-                % (os.path.dirname(me), versioneer_py)
+                % (os.path.dirname(my_path), versioneer_py)
             )
     except NameError:
         pass
@@ -338,14 +342,17 @@ def get_root():
 
 def get_config_from_root(root):
     """Read the project setup.cfg file to determine Versioneer config."""
-    # This might raise EnvironmentError (if setup.cfg is missing), or
+    # This might raise OSError (if setup.cfg is missing), or
     # configparser.NoSectionError (if it lacks a [versioneer] section), or
     # configparser.NoOptionError (if it lacks "VCS="). See the docstring at
     # the top of versioneer.py for instructions on writing your setup.cfg .
     setup_cfg = os.path.join(root, "setup.cfg")
-    parser = configparser.SafeConfigParser()
-    with open(setup_cfg, "r") as f:
-        parser.readfp(f)
+    parser = configparser.ConfigParser()
+    with open(setup_cfg, "r") as cfg_file:
+        if sys.version_info < (3, 0):
+            parser.readfp(cfg_file)
+        else:
+            parser.read_file(cfg_file)
     VCS = parser.get("versioneer", "VCS")  # mandatory
 
     def get(parser, name):
@@ -355,14 +362,25 @@ def get(parser, name):
 
     cfg = VersioneerConfig()
     cfg.VCS = VCS
-    cfg.style = get(parser, "style") or ""
-    cfg.versionfile_source = get(parser, "versionfile_source")
-    cfg.versionfile_build = get(parser, "versionfile_build")
-    cfg.tag_prefix = get(parser, "tag_prefix")
+    if sys.version_info < (3, 0):
+        cfg.style = get(parser, "style") or ""
+        cfg.versionfile_source = get(parser, "versionfile_source")
+        cfg.versionfile_build = get(parser, "versionfile_build")
+        cfg.tag_prefix = get(parser, "tag_prefix")
+        cfg.parentdir_prefix = get(parser, "parentdir_prefix")
+        cfg.verbose = get(parser, "verbose")
+    else:
+        # Dict-like interface for non-mandatory entries
+        section = parser["versioneer"]
+
+        cfg.style = section.get("style", "")
+        cfg.versionfile_source = section.get("versionfile_source")
+        cfg.versionfile_build = section.get("versionfile_build")
+        cfg.tag_prefix = section.get("tag_prefix")
+        cfg.parentdir_prefix = section.get("parentdir_prefix")
+        cfg.verbose = section.get("verbose")
     if cfg.tag_prefix in ("''", '""'):
         cfg.tag_prefix = ""
-    cfg.parentdir_prefix = get(parser, "parentdir_prefix")
-    cfg.verbose = get(parser, "verbose")
     return cfg
 
 
@@ -376,13 +394,11 @@ class NotThisMethod(Exception):
 
 
 def register_vcs_handler(vcs, method):  # decorator
-    """Decorator to mark a method as the handler for a particular VCS."""
+    """Create decorator to mark a method as the handler of a VCS."""
 
     def decorate(f):
         """Store f in HANDLERS[vcs][method]."""
-        if vcs not in HANDLERS:
-            HANDLERS[vcs] = {}
-        HANDLERS[vcs][method] = f
+        HANDLERS.setdefault(vcs, {})[method] = f
         return f
 
     return decorate
@@ -393,20 +409,20 @@ def run_command(
 ):
     """Call the given command(s)."""
     assert isinstance(commands, list)
-    p = None
-    for c in commands:
+    process = None
+    for command in commands:
         try:
-            dispcmd = str([c] + args)
+            dispcmd = str([command] + args)
             # remember shell=False, so use git.cmd on windows, not just git
-            p = subprocess.Popen(
-                [c] + args,
+            process = subprocess.Popen(
+                [command] + args,
                 cwd=cwd,
                 env=env,
                 stdout=subprocess.PIPE,
                 stderr=(subprocess.PIPE if hide_stderr else None),
             )
             break
-        except EnvironmentError:
+        except OSError:
             e = sys.exc_info()[1]
             if e.errno == errno.ENOENT:
                 continue
@@ -418,20 +434,18 @@ def run_command(
         if verbose:
             print("unable to find command, tried %s" % (commands,))
         return None, None
-    stdout = p.communicate()[0].strip()
-    if sys.version_info[0] >= 3:
-        stdout = stdout.decode()
-    if p.returncode != 0:
+    stdout = process.communicate()[0].strip().decode()
+    if process.returncode != 0:
         if verbose:
             print("unable to run %s (error)" % dispcmd)
             print("stdout was %s" % stdout)
-        return None, p.returncode
-    return stdout, p.returncode
+        return None, process.returncode
+    return stdout, process.returncode
 
 
 LONG_VERSION_PY[
     "git"
-] = '''
+] = r'''
 # This file helps to compute a version number in source trees obtained from
 # git-archive tarball (such as those provided by githubs download-from-tag
 # feature). Distribution tarballs (built by setup.py sdist) and build
@@ -439,7 +453,7 @@ def run_command(
 # that just contains the computed version number.
 
 # This file is released into the public domain. Generated by
-# versioneer-0.17 (https://github.com/warner/python-versioneer)
+# versioneer-0.21 (https://github.com/python-versioneer/python-versioneer)
 
 """Git implementation of _version.py."""
 
@@ -448,6 +462,7 @@ def run_command(
 import re
 import subprocess
 import sys
+from typing import Callable, Dict
 
 
 def get_keywords():
@@ -485,12 +500,12 @@ class NotThisMethod(Exception):
     """Exception raised if a method is not valid for the current scenario."""
 
 
-LONG_VERSION_PY = {}
-HANDLERS = {}
+LONG_VERSION_PY: Dict[str, str] = {}
+HANDLERS: Dict[str, Dict[str, Callable]] = {}
 
 
 def register_vcs_handler(vcs, method):  # decorator
-    """Decorator to mark a method as the handler for a particular VCS."""
+    """Create decorator to mark a method as the handler of a VCS."""
     def decorate(f):
         """Store f in HANDLERS[vcs][method]."""
         if vcs not in HANDLERS:
@@ -504,17 +519,17 @@ def run_command(commands, args, cwd=None, verbose=False, hide_stderr=False,
                 env=None):
     """Call the given command(s)."""
     assert isinstance(commands, list)
-    p = None
-    for c in commands:
+    process = None
+    for command in commands:
         try:
-            dispcmd = str([c] + args)
+            dispcmd = str([command] + args)
             # remember shell=False, so use git.cmd on windows, not just git
-            p = subprocess.Popen([c] + args, cwd=cwd, env=env,
-                                 stdout=subprocess.PIPE,
-                                 stderr=(subprocess.PIPE if hide_stderr
-                                         else None))
+            process = subprocess.Popen([command] + args, cwd=cwd, env=env,
+                                       stdout=subprocess.PIPE,
+                                       stderr=(subprocess.PIPE if hide_stderr
+                                               else None))
             break
-        except EnvironmentError:
+        except OSError:
             e = sys.exc_info()[1]
             if e.errno == errno.ENOENT:
                 continue
@@ -526,15 +541,13 @@ def run_command(commands, args, cwd=None, verbose=False, hide_stderr=False,
         if verbose:
             print("unable to find command, tried %%s" %% (commands,))
         return None, None
-    stdout = p.communicate()[0].strip()
-    if sys.version_info[0] >= 3:
-        stdout = stdout.decode()
-    if p.returncode != 0:
+    stdout = process.communicate()[0].strip().decode()
+    if process.returncode != 0:
         if verbose:
             print("unable to run %%s (error)" %% dispcmd)
             print("stdout was %%s" %% stdout)
-        return None, p.returncode
-    return stdout, p.returncode
+        return None, process.returncode
+    return stdout, process.returncode
 
 
 def versions_from_parentdir(parentdir_prefix, root, verbose):
@@ -546,15 +559,14 @@ def versions_from_parentdir(parentdir_prefix, root, verbose):
     """
     rootdirs = []
 
-    for i in range(3):
+    for _ in range(3):
         dirname = os.path.basename(root)
         if dirname.startswith(parentdir_prefix):
             return {"version": dirname[len(parentdir_prefix):],
                     "full-revisionid": None,
                     "dirty": False, "error": None, "date": None}
-        else:
-            rootdirs.append(root)
-            root = os.path.dirname(root)  # up a level
+        rootdirs.append(root)
+        root = os.path.dirname(root)  # up a level
 
     if verbose:
         print("Tried directories %%s but none started with prefix %%s" %%
@@ -571,22 +583,21 @@ def git_get_keywords(versionfile_abs):
     # _version.py.
     keywords = {}
     try:
-        f = open(versionfile_abs, "r")
-        for line in f.readlines():
-            if line.strip().startswith("git_refnames ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["refnames"] = mo.group(1)
-            if line.strip().startswith("git_full ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["full"] = mo.group(1)
-            if line.strip().startswith("git_date ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["date"] = mo.group(1)
-        f.close()
-    except EnvironmentError:
+        with open(versionfile_abs, "r") as fobj:
+            for line in fobj:
+                if line.strip().startswith("git_refnames ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["refnames"] = mo.group(1)
+                if line.strip().startswith("git_full ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["full"] = mo.group(1)
+                if line.strip().startswith("git_date ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["date"] = mo.group(1)
+    except OSError:
         pass
     return keywords
 
@@ -594,10 +605,14 @@ def git_get_keywords(versionfile_abs):
 @register_vcs_handler("git", "keywords")
 def git_versions_from_keywords(keywords, tag_prefix, verbose):
     """Get version information from git keywords."""
-    if not keywords:
-        raise NotThisMethod("no keywords at all, weird")
+    if "refnames" not in keywords:
+        raise NotThisMethod("Short version file found")
     date = keywords.get("date")
     if date is not None:
+        # Use only the last line.  Previous lines may contain GPG signature
+        # information.
+        date = date.splitlines()[-1]
+
         # git-2.2.0 added "%%cI", which expands to an ISO-8601 -compliant
         # datestamp. However we prefer "%%ci" (which expands to an "ISO-8601
         # -like" string, which we must then edit to make compliant), because
@@ -610,11 +625,11 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         if verbose:
             print("keywords are unexpanded, not using")
         raise NotThisMethod("unexpanded keywords, not a git-archive tarball")
-    refs = set([r.strip() for r in refnames.strip("()").split(",")])
+    refs = {r.strip() for r in refnames.strip("()").split(",")}
     # starting in git-1.8.3, tags are listed as "tag: foo-1.0" instead of
     # just "foo-1.0". If we see a "tag: " prefix, prefer those.
     TAG = "tag: "
-    tags = set([r[len(TAG):] for r in refs if r.startswith(TAG)])
+    tags = {r[len(TAG):] for r in refs if r.startswith(TAG)}
     if not tags:
         # Either we're using git < 1.8.3, or there really are no tags. We use
         # a heuristic: assume all version tags have a digit. The old git %%d
@@ -623,7 +638,7 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         # between branches and tags. By ignoring refnames without digits, we
         # filter out many common branch names like "release" and
         # "stabilization", as well as "HEAD" and "master".
-        tags = set([r for r in refs if re.search(r'\d', r)])
+        tags = {r for r in refs if re.search(r'\d', r)}
         if verbose:
             print("discarding '%%s', no digits" %% ",".join(refs - tags))
     if verbose:
@@ -632,6 +647,11 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         # sorting will prefer e.g. "2.0" over "2.0rc1"
         if ref.startswith(tag_prefix):
             r = ref[len(tag_prefix):]
+            # Filter out refs that exactly match prefix or that don't start
+            # with a number once the prefix is stripped (mostly a concern
+            # when prefix is '')
+            if not re.match(r'\d', r):
+                continue
             if verbose:
                 print("picking %%s" %% r)
             return {"version": r,
@@ -647,7 +667,7 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
 
 
 @register_vcs_handler("git", "pieces_from_vcs")
-def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
+def git_pieces_from_vcs(tag_prefix, root, verbose, runner=run_command):
     """Get version from 'git describe' in the root of the source tree.
 
     This only gets called if the git-archive 'subst' keywords were *not*
@@ -655,11 +675,13 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     version string, meaning we're inside a checked out source tree.
     """
     GITS = ["git"]
+    TAG_PREFIX_REGEX = "*"
     if sys.platform == "win32":
         GITS = ["git.cmd", "git.exe"]
+        TAG_PREFIX_REGEX = r"\*"
 
-    out, rc = run_command(GITS, ["rev-parse", "--git-dir"], cwd=root,
-                          hide_stderr=True)
+    _, rc = runner(GITS, ["rev-parse", "--git-dir"], cwd=root,
+                   hide_stderr=True)
     if rc != 0:
         if verbose:
             print("Directory %%s not under git control" %% root)
@@ -667,15 +689,16 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
 
     # if there is a tag matching tag_prefix, this yields TAG-NUM-gHEX[-dirty]
     # if there isn't one, this yields HEX[-dirty] (no NUM)
-    describe_out, rc = run_command(GITS, ["describe", "--tags", "--dirty",
-                                          "--always", "--long",
-                                          "--match", "%%s*" %% tag_prefix],
-                                   cwd=root)
+    describe_out, rc = runner(GITS, ["describe", "--tags", "--dirty",
+                                     "--always", "--long",
+                                     "--match",
+                                     "%%s%%s" %% (tag_prefix, TAG_PREFIX_REGEX)],
+                              cwd=root)
     # --long was added in git-1.5.5
     if describe_out is None:
         raise NotThisMethod("'git describe' failed")
     describe_out = describe_out.strip()
-    full_out, rc = run_command(GITS, ["rev-parse", "HEAD"], cwd=root)
+    full_out, rc = runner(GITS, ["rev-parse", "HEAD"], cwd=root)
     if full_out is None:
         raise NotThisMethod("'git rev-parse' failed")
     full_out = full_out.strip()
@@ -685,6 +708,39 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     pieces["short"] = full_out[:7]  # maybe improved later
     pieces["error"] = None
 
+    branch_name, rc = runner(GITS, ["rev-parse", "--abbrev-ref", "HEAD"],
+                             cwd=root)
+    # --abbrev-ref was added in git-1.6.3
+    if rc != 0 or branch_name is None:
+        raise NotThisMethod("'git rev-parse --abbrev-ref' returned error")
+    branch_name = branch_name.strip()
+
+    if branch_name == "HEAD":
+        # If we aren't exactly on a branch, pick a branch which represents
+        # the current commit. If all else fails, we are on a branchless
+        # commit.
+        branches, rc = runner(GITS, ["branch", "--contains"], cwd=root)
+        # --contains was added in git-1.5.4
+        if rc != 0 or branches is None:
+            raise NotThisMethod("'git branch --contains' returned error")
+        branches = branches.split("\n")
+
+        # Remove the first line if we're running detached
+        if "(" in branches[0]:
+            branches.pop(0)
+
+        # Strip off the leading "* " from the list of branches.
+        branches = [branch[2:] for branch in branches]
+        if "master" in branches:
+            branch_name = "master"
+        elif not branches:
+            branch_name = None
+        else:
+            # Pick the first branch that is returned. Good or bad.
+            branch_name = branches[0]
+
+    pieces["branch"] = branch_name
+
     # parse describe_out. It will be like TAG-NUM-gHEX[-dirty] or HEX[-dirty]
     # TAG might have hyphens.
     git_describe = describe_out
@@ -726,13 +782,14 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     else:
         # HEX: no tags
         pieces["closest-tag"] = None
-        count_out, rc = run_command(GITS, ["rev-list", "HEAD", "--count"],
-                                    cwd=root)
+        count_out, rc = runner(GITS, ["rev-list", "HEAD", "--count"], cwd=root)
         pieces["distance"] = int(count_out)  # total number of commits
 
     # commit date: see ISO-8601 comment in git_versions_from_keywords()
-    date = run_command(GITS, ["show", "-s", "--format=%%ci", "HEAD"],
-                       cwd=root)[0].strip()
+    date = runner(GITS, ["show", "-s", "--format=%%ci", "HEAD"], cwd=root)[0].strip()
+    # Use only the last line.  Previous lines may contain GPG signature
+    # information.
+    date = date.splitlines()[-1]
     pieces["date"] = date.strip().replace(" ", "T", 1).replace(" ", "", 1)
 
     return pieces
@@ -770,19 +827,67 @@ def render_pep440(pieces):
     return rendered
 
 
-def render_pep440_pre(pieces):
-    """TAG[.post.devDISTANCE] -- No -dirty.
+def render_pep440_branch(pieces):
+    """TAG[[.dev0]+DISTANCE.gHEX[.dirty]] .
+
+    The ".dev0" means not master branch. Note that .dev0 sorts backwards
+    (a feature branch will appear "older" than the master branch).
 
     Exceptions:
-    1: no tags. 0.post.devDISTANCE
+    1: no tags. 0[.dev0]+untagged.DISTANCE.gHEX[.dirty]
     """
     if pieces["closest-tag"]:
         rendered = pieces["closest-tag"]
+        if pieces["distance"] or pieces["dirty"]:
+            if pieces["branch"] != "master":
+                rendered += ".dev0"
+            rendered += plus_or_dot(pieces)
+            rendered += "%%d.g%%s" %% (pieces["distance"], pieces["short"])
+            if pieces["dirty"]:
+                rendered += ".dirty"
+    else:
+        # exception #1
+        rendered = "0"
+        if pieces["branch"] != "master":
+            rendered += ".dev0"
+        rendered += "+untagged.%%d.g%%s" %% (pieces["distance"],
+                                          pieces["short"])
+        if pieces["dirty"]:
+            rendered += ".dirty"
+    return rendered
+
+
+def pep440_split_post(ver):
+    """Split pep440 version string at the post-release segment.
+
+    Returns the release segments before the post-release and the
+    post-release version number (or -1 if no post-release segment is present).
+    """
+    vc = str.split(ver, ".post")
+    return vc[0], int(vc[1] or 0) if len(vc) == 2 else None
+
+
+def render_pep440_pre(pieces):
+    """TAG[.postN.devDISTANCE] -- No -dirty.
+
+    Exceptions:
+    1: no tags. 0.post0.devDISTANCE
+    """
+    if pieces["closest-tag"]:
         if pieces["distance"]:
-            rendered += ".post.dev%%d" %% pieces["distance"]
+            # update the post release segment
+            tag_version, post_version = pep440_split_post(pieces["closest-tag"])
+            rendered = tag_version
+            if post_version is not None:
+                rendered += ".post%%d.dev%%d" %% (post_version+1, pieces["distance"])
+            else:
+                rendered += ".post0.dev%%d" %% (pieces["distance"])
+        else:
+            # no commits, use the tag as the version
+            rendered = pieces["closest-tag"]
     else:
         # exception #1
-        rendered = "0.post.dev%%d" %% pieces["distance"]
+        rendered = "0.post0.dev%%d" %% pieces["distance"]
     return rendered
 
 
@@ -813,12 +918,41 @@ def render_pep440_post(pieces):
     return rendered
 
 
+def render_pep440_post_branch(pieces):
+    """TAG[.postDISTANCE[.dev0]+gHEX[.dirty]] .
+
+    The ".dev0" means not master branch.
+
+    Exceptions:
+    1: no tags. 0.postDISTANCE[.dev0]+gHEX[.dirty]
+    """
+    if pieces["closest-tag"]:
+        rendered = pieces["closest-tag"]
+        if pieces["distance"] or pieces["dirty"]:
+            rendered += ".post%%d" %% pieces["distance"]
+            if pieces["branch"] != "master":
+                rendered += ".dev0"
+            rendered += plus_or_dot(pieces)
+            rendered += "g%%s" %% pieces["short"]
+            if pieces["dirty"]:
+                rendered += ".dirty"
+    else:
+        # exception #1
+        rendered = "0.post%%d" %% pieces["distance"]
+        if pieces["branch"] != "master":
+            rendered += ".dev0"
+        rendered += "+g%%s" %% pieces["short"]
+        if pieces["dirty"]:
+            rendered += ".dirty"
+    return rendered
+
+
 def render_pep440_old(pieces):
     """TAG[.postDISTANCE[.dev0]] .
 
     The ".dev0" means dirty.
 
-    Eexceptions:
+    Exceptions:
     1: no tags. 0.postDISTANCE[.dev0]
     """
     if pieces["closest-tag"]:
@@ -889,10 +1023,14 @@ def render(pieces, style):
 
     if style == "pep440":
         rendered = render_pep440(pieces)
+    elif style == "pep440-branch":
+        rendered = render_pep440_branch(pieces)
     elif style == "pep440-pre":
         rendered = render_pep440_pre(pieces)
     elif style == "pep440-post":
         rendered = render_pep440_post(pieces)
+    elif style == "pep440-post-branch":
+        rendered = render_pep440_post_branch(pieces)
     elif style == "pep440-old":
         rendered = render_pep440_old(pieces)
     elif style == "git-describe":
@@ -928,7 +1066,7 @@ def get_versions():
         # versionfile_source is the relative path from the top of the source
         # tree (where the .git directory might live) to this file. Invert
         # this to find the root from __file__.
-        for i in cfg.versionfile_source.split('/'):
+        for _ in cfg.versionfile_source.split('/'):
             root = os.path.dirname(root)
     except NameError:
         return {"version": "0+unknown", "full-revisionid": None,
@@ -963,22 +1101,21 @@ def git_get_keywords(versionfile_abs):
     # _version.py.
     keywords = {}
     try:
-        f = open(versionfile_abs, "r")
-        for line in f.readlines():
-            if line.strip().startswith("git_refnames ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["refnames"] = mo.group(1)
-            if line.strip().startswith("git_full ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["full"] = mo.group(1)
-            if line.strip().startswith("git_date ="):
-                mo = re.search(r'=\s*"(.*)"', line)
-                if mo:
-                    keywords["date"] = mo.group(1)
-        f.close()
-    except EnvironmentError:
+        with open(versionfile_abs, "r") as fobj:
+            for line in fobj:
+                if line.strip().startswith("git_refnames ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["refnames"] = mo.group(1)
+                if line.strip().startswith("git_full ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["full"] = mo.group(1)
+                if line.strip().startswith("git_date ="):
+                    mo = re.search(r'=\s*"(.*)"', line)
+                    if mo:
+                        keywords["date"] = mo.group(1)
+    except OSError:
         pass
     return keywords
 
@@ -986,10 +1123,14 @@ def git_get_keywords(versionfile_abs):
 @register_vcs_handler("git", "keywords")
 def git_versions_from_keywords(keywords, tag_prefix, verbose):
     """Get version information from git keywords."""
-    if not keywords:
-        raise NotThisMethod("no keywords at all, weird")
+    if "refnames" not in keywords:
+        raise NotThisMethod("Short version file found")
     date = keywords.get("date")
     if date is not None:
+        # Use only the last line.  Previous lines may contain GPG signature
+        # information.
+        date = date.splitlines()[-1]
+
         # git-2.2.0 added "%cI", which expands to an ISO-8601 -compliant
         # datestamp. However we prefer "%ci" (which expands to an "ISO-8601
         # -like" string, which we must then edit to make compliant), because
@@ -1002,11 +1143,11 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         if verbose:
             print("keywords are unexpanded, not using")
         raise NotThisMethod("unexpanded keywords, not a git-archive tarball")
-    refs = set([r.strip() for r in refnames.strip("()").split(",")])
+    refs = {r.strip() for r in refnames.strip("()").split(",")}
     # starting in git-1.8.3, tags are listed as "tag: foo-1.0" instead of
     # just "foo-1.0". If we see a "tag: " prefix, prefer those.
     TAG = "tag: "
-    tags = set([r[len(TAG) :] for r in refs if r.startswith(TAG)])
+    tags = {r[len(TAG) :] for r in refs if r.startswith(TAG)}
     if not tags:
         # Either we're using git < 1.8.3, or there really are no tags. We use
         # a heuristic: assume all version tags have a digit. The old git %d
@@ -1015,7 +1156,7 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         # between branches and tags. By ignoring refnames without digits, we
         # filter out many common branch names like "release" and
         # "stabilization", as well as "HEAD" and "master".
-        tags = set([r for r in refs if re.search(r"\d", r)])
+        tags = {r for r in refs if re.search(r"\d", r)}
         if verbose:
             print("discarding '%s', no digits" % ",".join(refs - tags))
     if verbose:
@@ -1024,6 +1165,11 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
         # sorting will prefer e.g. "2.0" over "2.0rc1"
         if ref.startswith(tag_prefix):
             r = ref[len(tag_prefix) :]
+            # Filter out refs that exactly match prefix or that don't start
+            # with a number once the prefix is stripped (mostly a concern
+            # when prefix is '')
+            if not re.match(r"\d", r):
+                continue
             if verbose:
                 print("picking %s" % r)
             return {
@@ -1046,7 +1192,7 @@ def git_versions_from_keywords(keywords, tag_prefix, verbose):
 
 
 @register_vcs_handler("git", "pieces_from_vcs")
-def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
+def git_pieces_from_vcs(tag_prefix, root, verbose, runner=run_command):
     """Get version from 'git describe' in the root of the source tree.
 
     This only gets called if the git-archive 'subst' keywords were *not*
@@ -1054,10 +1200,12 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     version string, meaning we're inside a checked out source tree.
     """
     GITS = ["git"]
+    TAG_PREFIX_REGEX = "*"
     if sys.platform == "win32":
         GITS = ["git.cmd", "git.exe"]
+        TAG_PREFIX_REGEX = r"\*"
 
-    out, rc = run_command(
+    _, rc = runner(
         GITS, ["rev-parse", "--git-dir"], cwd=root, hide_stderr=True
     )
     if rc != 0:
@@ -1067,7 +1215,7 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
 
     # if there is a tag matching tag_prefix, this yields TAG-NUM-gHEX[-dirty]
     # if there isn't one, this yields HEX[-dirty] (no NUM)
-    describe_out, rc = run_command(
+    describe_out, rc = runner(
         GITS,
         [
             "describe",
@@ -1076,7 +1224,7 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
             "--always",
             "--long",
             "--match",
-            "%s*" % tag_prefix,
+            "%s%s" % (tag_prefix, TAG_PREFIX_REGEX),
         ],
         cwd=root,
     )
@@ -1084,7 +1232,7 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     if describe_out is None:
         raise NotThisMethod("'git describe' failed")
     describe_out = describe_out.strip()
-    full_out, rc = run_command(GITS, ["rev-parse", "HEAD"], cwd=root)
+    full_out, rc = runner(GITS, ["rev-parse", "HEAD"], cwd=root)
     if full_out is None:
         raise NotThisMethod("'git rev-parse' failed")
     full_out = full_out.strip()
@@ -1094,6 +1242,40 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     pieces["short"] = full_out[:7]  # maybe improved later
     pieces["error"] = None
 
+    branch_name, rc = runner(
+        GITS, ["rev-parse", "--abbrev-ref", "HEAD"], cwd=root
+    )
+    # --abbrev-ref was added in git-1.6.3
+    if rc != 0 or branch_name is None:
+        raise NotThisMethod("'git rev-parse --abbrev-ref' returned error")
+    branch_name = branch_name.strip()
+
+    if branch_name == "HEAD":
+        # If we aren't exactly on a branch, pick a branch which represents
+        # the current commit. If all else fails, we are on a branchless
+        # commit.
+        branches, rc = runner(GITS, ["branch", "--contains"], cwd=root)
+        # --contains was added in git-1.5.4
+        if rc != 0 or branches is None:
+            raise NotThisMethod("'git branch --contains' returned error")
+        branches = branches.split("\n")
+
+        # Remove the first line if we're running detached
+        if "(" in branches[0]:
+            branches.pop(0)
+
+        # Strip off the leading "* " from the list of branches.
+        branches = [branch[2:] for branch in branches]
+        if "master" in branches:
+            branch_name = "master"
+        elif not branches:
+            branch_name = None
+        else:
+            # Pick the first branch that is returned. Good or bad.
+            branch_name = branches[0]
+
+    pieces["branch"] = branch_name
+
     # parse describe_out. It will be like TAG-NUM-gHEX[-dirty] or HEX[-dirty]
     # TAG might have hyphens.
     git_describe = describe_out
@@ -1138,15 +1320,16 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
     else:
         # HEX: no tags
         pieces["closest-tag"] = None
-        count_out, rc = run_command(
-            GITS, ["rev-list", "HEAD", "--count"], cwd=root
-        )
+        count_out, rc = runner(GITS, ["rev-list", "HEAD", "--count"], cwd=root)
         pieces["distance"] = int(count_out)  # total number of commits
 
     # commit date: see ISO-8601 comment in git_versions_from_keywords()
-    date = run_command(GITS, ["show", "-s", "--format=%ci", "HEAD"], cwd=root)[
+    date = runner(GITS, ["show", "-s", "--format=%ci", "HEAD"], cwd=root)[
         0
     ].strip()
+    # Use only the last line.  Previous lines may contain GPG signature
+    # information.
+    date = date.splitlines()[-1]
     pieces["date"] = date.strip().replace(" ", "T", 1).replace(" ", "", 1)
 
     return pieces
@@ -1165,27 +1348,26 @@ def do_vcs_install(manifest_in, versionfile_source, ipy):
     if ipy:
         files.append(ipy)
     try:
-        me = __file__
-        if me.endswith(".pyc") or me.endswith(".pyo"):
-            me = os.path.splitext(me)[0] + ".py"
-        versioneer_file = os.path.relpath(me)
+        my_path = __file__
+        if my_path.endswith(".pyc") or my_path.endswith(".pyo"):
+            my_path = os.path.splitext(my_path)[0] + ".py"
+        versioneer_file = os.path.relpath(my_path)
     except NameError:
         versioneer_file = "versioneer.py"
     files.append(versioneer_file)
     present = False
     try:
-        f = open(".gitattributes", "r")
-        for line in f.readlines():
-            if line.strip().startswith(versionfile_source):
-                if "export-subst" in line.strip().split()[1:]:
-                    present = True
-        f.close()
-    except EnvironmentError:
+        with open(".gitattributes", "r") as fobj:
+            for line in fobj:
+                if line.strip().startswith(versionfile_source):
+                    if "export-subst" in line.strip().split()[1:]:
+                        present = True
+                        break
+    except OSError:
         pass
     if not present:
-        f = open(".gitattributes", "a+")
-        f.write("%s export-subst\n" % versionfile_source)
-        f.close()
+        with open(".gitattributes", "a+") as fobj:
+            fobj.write("{0} export-subst\n".format(versionfile_source))
         files.append(".gitattributes")
     run_command(GITS, ["add", "--"] + files)
 
@@ -1199,7 +1381,7 @@ def versions_from_parentdir(parentdir_prefix, root, verbose):
     """
     rootdirs = []
 
-    for i in range(3):
+    for _ in range(3):
         dirname = os.path.basename(root)
         if dirname.startswith(parentdir_prefix):
             return {
@@ -1209,9 +1391,8 @@ def versions_from_parentdir(parentdir_prefix, root, verbose):
                 "error": None,
                 "date": None,
             }
-        else:
-            rootdirs.append(root)
-            root = os.path.dirname(root)  # up a level
+        rootdirs.append(root)
+        root = os.path.dirname(root)  # up a level
 
     if verbose:
         print(
@@ -1222,7 +1403,7 @@ def versions_from_parentdir(parentdir_prefix, root, verbose):
 
 
 SHORT_VERSION_PY = """
-# This file was generated by 'versioneer.py' (0.17) from
+# This file was generated by 'versioneer.py' (0.21) from
 # revision-control system data, or from the parent directory name of an
 # unpacked source archive. Distribution tarballs contain a pre-generated copy
 # of this file.
@@ -1244,7 +1425,7 @@ def versions_from_file(filename):
     try:
         with open(filename) as f:
             contents = f.read()
-    except EnvironmentError:
+    except OSError:
         raise NotThisMethod("unable to read _version.py")
     mo = re.search(
         r"version_json = '''\n(.*)'''  # END VERSION_JSON",
@@ -1305,19 +1486,71 @@ def render_pep440(pieces):
     return rendered
 
 
-def render_pep440_pre(pieces):
-    """TAG[.post.devDISTANCE] -- No -dirty.
+def render_pep440_branch(pieces):
+    """TAG[[.dev0]+DISTANCE.gHEX[.dirty]] .
+
+    The ".dev0" means not master branch. Note that .dev0 sorts backwards
+    (a feature branch will appear "older" than the master branch).
 
     Exceptions:
-    1: no tags. 0.post.devDISTANCE
+    1: no tags. 0[.dev0]+untagged.DISTANCE.gHEX[.dirty]
     """
     if pieces["closest-tag"]:
         rendered = pieces["closest-tag"]
+        if pieces["distance"] or pieces["dirty"]:
+            if pieces["branch"] != "master":
+                rendered += ".dev0"
+            rendered += plus_or_dot(pieces)
+            rendered += "%d.g%s" % (pieces["distance"], pieces["short"])
+            if pieces["dirty"]:
+                rendered += ".dirty"
+    else:
+        # exception #1
+        rendered = "0"
+        if pieces["branch"] != "master":
+            rendered += ".dev0"
+        rendered += "+untagged.%d.g%s" % (pieces["distance"], pieces["short"])
+        if pieces["dirty"]:
+            rendered += ".dirty"
+    return rendered
+
+
+def pep440_split_post(ver):
+    """Split pep440 version string at the post-release segment.
+
+    Returns the release segments before the post-release and the
+    post-release version number (or -1 if no post-release segment is present).
+    """
+    vc = str.split(ver, ".post")
+    return vc[0], int(vc[1] or 0) if len(vc) == 2 else None
+
+
+def render_pep440_pre(pieces):
+    """TAG[.postN.devDISTANCE] -- No -dirty.
+
+    Exceptions:
+    1: no tags. 0.post0.devDISTANCE
+    """
+    if pieces["closest-tag"]:
         if pieces["distance"]:
-            rendered += ".post.dev%d" % pieces["distance"]
+            # update the post release segment
+            tag_version, post_version = pep440_split_post(
+                pieces["closest-tag"]
+            )
+            rendered = tag_version
+            if post_version is not None:
+                rendered += ".post%d.dev%d" % (
+                    post_version + 1,
+                    pieces["distance"],
+                )
+            else:
+                rendered += ".post0.dev%d" % (pieces["distance"])
+        else:
+            # no commits, use the tag as the version
+            rendered = pieces["closest-tag"]
     else:
         # exception #1
-        rendered = "0.post.dev%d" % pieces["distance"]
+        rendered = "0.post0.dev%d" % pieces["distance"]
     return rendered
 
 
@@ -1348,12 +1581,41 @@ def render_pep440_post(pieces):
     return rendered
 
 
+def render_pep440_post_branch(pieces):
+    """TAG[.postDISTANCE[.dev0]+gHEX[.dirty]] .
+
+    The ".dev0" means not master branch.
+
+    Exceptions:
+    1: no tags. 0.postDISTANCE[.dev0]+gHEX[.dirty]
+    """
+    if pieces["closest-tag"]:
+        rendered = pieces["closest-tag"]
+        if pieces["distance"] or pieces["dirty"]:
+            rendered += ".post%d" % pieces["distance"]
+            if pieces["branch"] != "master":
+                rendered += ".dev0"
+            rendered += plus_or_dot(pieces)
+            rendered += "g%s" % pieces["short"]
+            if pieces["dirty"]:
+                rendered += ".dirty"
+    else:
+        # exception #1
+        rendered = "0.post%d" % pieces["distance"]
+        if pieces["branch"] != "master":
+            rendered += ".dev0"
+        rendered += "+g%s" % pieces["short"]
+        if pieces["dirty"]:
+            rendered += ".dirty"
+    return rendered
+
+
 def render_pep440_old(pieces):
     """TAG[.postDISTANCE[.dev0]] .
 
     The ".dev0" means dirty.
 
-    Eexceptions:
+    Exceptions:
     1: no tags. 0.postDISTANCE[.dev0]
     """
     if pieces["closest-tag"]:
@@ -1426,10 +1688,14 @@ def render(pieces, style):
 
     if style == "pep440":
         rendered = render_pep440(pieces)
+    elif style == "pep440-branch":
+        rendered = render_pep440_branch(pieces)
     elif style == "pep440-pre":
         rendered = render_pep440_pre(pieces)
     elif style == "pep440-post":
         rendered = render_pep440_post(pieces)
+    elif style == "pep440-post-branch":
+        rendered = render_pep440_post_branch(pieces)
     elif style == "pep440-old":
         rendered = render_pep440_old(pieces)
     elif style == "git-describe":
@@ -1538,8 +1804,12 @@ def get_version():
     return get_versions()["version"]
 
 
-def get_cmdclass():
-    """Get the custom setuptools/distutils subclasses used by Versioneer."""
+def get_cmdclass(cmdclass=None):
+    """Get the custom setuptools/distutils subclasses used by Versioneer.
+
+    If the package uses a different cmdclass (e.g. one from numpy), it
+    should be provide as an argument.
+    """
     if "versioneer" in sys.modules:
         del sys.modules["versioneer"]
         # this fixes the "python setup.py develop" case (also 'install' and
@@ -1553,9 +1823,9 @@ def get_cmdclass():
         # parent is protected against the child's "import versioneer". By
         # removing ourselves from sys.modules here, before the child build
         # happens, we protect the child from the parent's versioneer too.
-        # Also see https://github.com/warner/python-versioneer/issues/52
+        # Also see https://github.com/python-versioneer/python-versioneer/issues/52
 
-    cmds = {}
+    cmds = {} if cmdclass is None else cmdclass.copy()
 
     # we add "version" to both distutils and setuptools
     from distutils.core import Command
@@ -1598,7 +1868,9 @@ def run(self):
     #  setup.py egg_info -> ?
 
     # we override different "build_py" commands for both environments
-    if "setuptools" in sys.modules:
+    if "build_py" in cmds:
+        _build_py = cmds["build_py"]
+    elif "setuptools" in sys.modules:
         from setuptools.command.build_py import build_py as _build_py
     else:
         from distutils.command.build_py import build_py as _build_py
@@ -1620,6 +1892,35 @@ def run(self):
 
     cmds["build_py"] = cmd_build_py
 
+    if "build_ext" in cmds:
+        _build_ext = cmds["build_ext"]
+    elif "setuptools" in sys.modules:
+        from setuptools.command.build_ext import build_ext as _build_ext
+    else:
+        from distutils.command.build_ext import build_ext as _build_ext
+
+    class cmd_build_ext(_build_ext):
+        def run(self):
+            root = get_root()
+            cfg = get_config_from_root(root)
+            versions = get_versions()
+            _build_ext.run(self)
+            if self.inplace:
+                # build_ext --inplace will only build extensions in
+                # build/lib<..> dir with no _version.py to write to.
+                # As in place builds will already have a _version.py
+                # in the module dir, we do not need to write one.
+                return
+            # now locate _version.py in the new build/ directory and replace
+            # it with an updated value
+            target_versionfile = os.path.join(
+                self.build_lib, cfg.versionfile_build
+            )
+            print("UPDATING %s" % target_versionfile)
+            write_to_version_file(target_versionfile, versions)
+
+    cmds["build_ext"] = cmd_build_ext
+
     if "cx_Freeze" in sys.modules:  # cx_freeze enabled?
         from cx_Freeze.dist import build_exe as _build_exe
 
@@ -1658,10 +1959,7 @@ def run(self):
         del cmds["build_py"]
 
     if "py2exe" in sys.modules:  # py2exe enabled?
-        try:
-            from py2exe.distutils_buildexe import py2exe as _py2exe  # py3
-        except ImportError:
-            from py2exe.build_exe import py2exe as _py2exe  # py2
+        from py2exe.distutils_buildexe import py2exe as _py2exe
 
         class cmd_py2exe(_py2exe):
             def run(self):
@@ -1690,7 +1988,9 @@ def run(self):
         cmds["py2exe"] = cmd_py2exe
 
     # we override different "sdist" commands for both environments
-    if "setuptools" in sys.modules:
+    if "sdist" in cmds:
+        _sdist = cmds["sdist"]
+    elif "setuptools" in sys.modules:
         from setuptools.command.sdist import sdist as _sdist
     else:
         from distutils.command.sdist import sdist as _sdist
@@ -1759,24 +2059,29 @@ def make_release_tree(self, base_dir, files):
 
 """
 
-INIT_PY_SNIPPET = """
+OLD_SNIPPET = """
 from ._version import get_versions
 __version__ = get_versions()['version']
 del get_versions
 """
 
+INIT_PY_SNIPPET = """
+from . import {0}
+__version__ = {0}.get_versions()['version']
+"""
+
 
 def do_setup():
-    """Main VCS-independent setup function for installing Versioneer."""
+    """Do main VCS-independent setup function for installing Versioneer."""
     root = get_root()
     try:
         cfg = get_config_from_root(root)
     except (
-        EnvironmentError,
+        OSError,
         configparser.NoSectionError,
         configparser.NoOptionError,
     ) as e:
-        if isinstance(e, (EnvironmentError, configparser.NoSectionError)):
+        if isinstance(e, (OSError, configparser.NoSectionError)):
             print(
                 "Adding sample versioneer config to setup.cfg", file=sys.stderr
             )
@@ -1804,12 +2109,18 @@ def do_setup():
         try:
             with open(ipy, "r") as f:
                 old = f.read()
-        except EnvironmentError:
+        except OSError:
             old = ""
-        if INIT_PY_SNIPPET not in old:
+        module = os.path.splitext(os.path.basename(cfg.versionfile_source))[0]
+        snippet = INIT_PY_SNIPPET.format(module)
+        if OLD_SNIPPET in old:
+            print(" replacing boilerplate in %s" % ipy)
+            with open(ipy, "w") as f:
+                f.write(old.replace(OLD_SNIPPET, snippet))
+        elif snippet not in old:
             print(" appending to %s" % ipy)
             with open(ipy, "a") as f:
-                f.write(INIT_PY_SNIPPET)
+                f.write(snippet)
         else:
             print(" %s unmodified" % ipy)
     else:
@@ -1828,7 +2139,7 @@ def do_setup():
                 if line.startswith("include "):
                     for include in line.split()[1:]:
                         simple_includes.add(include)
-    except EnvironmentError:
+    except OSError:
         pass
     # That doesn't cover everything MANIFEST.in can do
     # (http://docs.python.org/2/distutils/sourcedist.html#commands), so