Add typing_extensions subfolder

This pull request adds a 'typing_exensions' subproject to 'typing'. The
'typing_extensions' module backports any new additions to 'typing'
for Python 3.5+ users who are using older versions of 'typing' that were
bundled with their standard library (and so can't update to the latest
versions).

See python#435 for motivation and
additional context.

typing_extensions/.gitignore

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+MANIFEST
+build/
+dist/
+.tox/
+.idea/
+.cache/
+__pycache__/
+.mypy_cache/
+tmp/
+*.swp
+*.pyc

typing_extensions/README.md

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+# Typing Extensions
+
+The `typing_extensions` module contains backports of recent changes
+to the `typing` module that were not present in older versions of
+`typing`.
+
+This module is intended to be used mainly by people who are using
+Python 3.5+, where the `typing` module is a part of the standard
+library and cannot be updated to the latest version on PyPi.
+
+Users of other Python versions should continue to install and use
+use the `typing` module from PyPi instead of using this one, unless
+they are specifically writing code intended to be compatible with
+multiple versions of Python.
+
+## Backported items
+
+This module contains the following backported items:
+
+### All Python versions:
+
+- `ClassVar`
+- `Collection`
+- `ContextManager`
+- `Counter`
+- `DefaultDict`
+- `Deque`
+- `NewType`
+- `NoReturn`
+- `overload` (note that older versions of `typing` only let you use `overload` in stubs)
+- `Text`
+- `Type`
+- `TYPE_CHECKING`
+
+### Python 3.3+ only:
+
+- `ChainMap`
+
+### Python 3.5+ only:
+
+- `AsyncIterable`
+- `AsyncIterator`
+- `AsyncContextManager`
+- `Awaitable`
+- `Coroutine`
+
+### Python 3.6+ only:
+
+- `AsyncGenerator`
+
+## Other Notes and Limitations
+
+There are a few types who's interface was modified between different
+versions of typing. For example, `typing.Sequence` was modified to
+subclass `typing.Reversible` as of Python 3.5.3.
+
+These changes are _not_ backported to prevent subtle compatibility
+issues when mixing the differing implementations of modified classes.
+
+## Running tests
+
+There are two different ways to test this module. The first is to simply run
+each individual Python interpreter against `test_typing_extensions.py` in the 
+`src_py2` and `src_py3` folders.
+
+However, because multiple versions of Python for each individual release
+can be onerous, you can instead run `run_tests.py` using a single Python
+interpreter. The `run_tests.py` file will essentially "modify" the standard
+library by changing `PYTHONPATH` to point to individual folders in the 
+`test_data` repo.
+
+Each individual folder contains a snapshot of the source code for the 
+`collections`, `typing,` and `abc` modules for that given release, letting us
+test `typing` against those particular implementations.
+
+`run_tests.py` will assume that you have Python 3.6.1 and a reasonably
+modern version of Python 2.7 installed on your system, aliased to 
+`py -2.7` and `py -3.6` on Windows, and `python` and `python3` on Linux and
+Mac.

typing_extensions/run_tests.py

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+#!/usr/bin/env python
+
+from typing import List, Iterator, Tuple
+from contextlib import contextmanager
+import glob
+import os
+import os.path
+import shutil
+import subprocess
+import sys
+import textwrap
+
+CORE_FILES_2 = [
+        "./src_py2/typing_extensions.py", 
+        "./src_py2/test_typing_extensions.py"
+]
+CORE_FILES_3 = [
+        "./src_py3/typing_extensions.py", 
+        "./src_py3/test_typing_extensions.py"
+]
+TEST_DIR = "test_data"
+
+if sys.platform.startswith('win32'):
+    PYTHON2 = "py -2.7"
+    PYTHON3 = "py -3.6"
+else:
+    PYTHON2 = "python"
+    PYTHON3 = "python3"
+
+
+def get_test_dirs() -> List[str]:
+    """Get all folders to test inside TEST_DIR."""
+    return list(glob.glob(os.path.join(TEST_DIR, "*")))
+
+
+@contextmanager
+def temp_copy(src_files: List[str], dest_dir: str) -> Iterator[None]:
+    """
+    A context manager that temporarily copies the given files to the
+    given destination directory, and deletes those temp files upon
+    exiting.
+    """
+    # Copy
+    for src_path in src_files:
+        shutil.copy(src_path, dest_dir)
+
+    yield
+
+    # Delete
+    for src_path in src_files:
+        dst_path = os.path.join(dest_dir, os.path.basename(src_path))
+        os.remove(dst_path)
+
+
+@contextmanager
+def change_directory(dir_path: str) -> Iterator[None]:
+    """
+    A context manager that temporarily changes the working directory
+    to the specified directory, and changes back to the original
+    upon exiting.
+    """
+    original = os.getcwd()
+    os.chdir(dir_path)
+
+    yield
+
+    os.chdir(original)
+
+
+def run_shell(command: str) -> Tuple[bool, str]:
+    env = os.environ.copy()
+    env["PYTHONPATH"] = ":".join([os.getcwd(), env["PYTHONPATH"], env["PATH"]])
+    out = subprocess.run(
+            command,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT,
+            shell=True,
+            env=env)
+    success = out.returncode == 0
+    stdout = '' if out.stdout is None else out.stdout.decode('utf-8')
+    return (success, stdout)
+
+
+def main() -> int:
+    test_dirs = get_test_dirs()
+    exit_code = 0
+    for test_dir in test_dirs:
+        _, version_number = test_dir.split('-')
+        py2 = version_number.startswith("2")
+        print("Testing Python {}".format(version_number))
+
+        core_files = CORE_FILES_2 if py2 else CORE_FILES_3
+        python_exe = PYTHON2 if py2 else PYTHON3
+
+        with temp_copy(core_files, test_dir), change_directory(test_dir):
+            success, output = run_shell("{} {} {}".format(
+                python_exe, 
+                "test_typing_extensions.py",
+                version_number))
+            if success:
+                print("   All tests passed!")
+            else:
+                print(textwrap.indent(output, "    "))
+                exit_code = 1
+    return exit_code
+
+
+if __name__ == '__main__':
+    sys.exit(main())
+

typing_extensions/setup.py

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+#!/usr/bin/env python
+# coding: utf-8
+
+import sys
+from distutils.core import setup
+
+if sys.version_info < (2, 7, 0) or (3, 0, 0) <= sys.version_info < (3, 3, 0):
+    sys.stderr.write('ERROR: You need Python 2.7 or 3.3+ '
+                     'to install the typing package.\n')
+    exit(1)
+
+version = '3.6.1'
+description = 'Type Hint backports for Python 3.5+'
+long_description = '''\
+Typing -- Type Hints for Python
+
+This is a backport of the standard library typing module to Python
+versions 3.5+. The typing module has seen several changes since it was
+first added in Python 3.5.0, which means people who are using 3.5.0+
+but are unable to upgrade to the latest version of Python are unable
+to take advantage of some new features of the typing library, such as
+typing.Type or typing.Coroutine.
+
+This module allows those users to use the latest additions to the typing
+module without worrying about naming conflicts with the standard library.
+Users of Python 2.7, 3.3, and 3.4 should install the typing module
+from pypi and use that directly, except when writing code that needs to
+be compatible across multiple versions of Python.
+'''
+
+classifiers = [
+    'Development Status :: 5 - Production/Stable',
+    'Environment :: Console',
+    'Intended Audience :: Developers',
+    'License :: OSI Approved :: Python Software Foundation License',
+    'Operating System :: OS Independent',
+    'Programming Language :: Python :: 2.7',
+    'Programming Language :: Python :: 3.3',
+    'Programming Language :: Python :: 3.4',
+    'Programming Language :: Python :: 3.5',
+    'Programming Language :: Python :: 3.6',
+    'Topic :: Software Development',
+]
+
+if sys.version_info.major == 2:
+    package_dir = 'src_py2'
+elif sys.version_info.major == 3:
+    package_dir = 'src_py3'
+else:
+    raise AssertionError()
+
+install_requires = []
+if sys.version_info < (3, 5):
+    install_requires.append('typing >= 3.6.1')
+
+setup(name='typing_extensions',
+      version=version,
+      description=description,
+      long_description=long_description,
+      author='Guido van Rossum, Jukka Lehtosalo, Lukasz Langa, Michael Lee',
+      author_email='jukka.lehtosalo@iki.fi',
+      # TODO: Change URL
+      url='https://github.com/michael0x2a/typing_extensions',
+      license='PSF',
+      keywords='typing function annotations type hints hinting checking '
+               'checker typehints typehinting typechecking backport',
+      package_dir={'': package_dir},
+      py_modules=['typing_extensions'],
+      classifiers=classifiers,
+      install_requires=install_requires,
+)