Python3.6 idioms (#3419)

* pyupgrade --py36-plus

* Update xarray/core/nputils.py

Co-Authored-By: crusaderky <crusaderky@gmail.com>

* Update xarray/core/parallel.py

Co-Authored-By: crusaderky <crusaderky@gmail.com>

* Update xarray/tests/test_cftime_offsets.py

Co-Authored-By: crusaderky <crusaderky@gmail.com>

* Update xarray/tests/test_cftime_offsets.py

Co-Authored-By: crusaderky <crusaderky@gmail.com>

doc/gallery/plot_cartopy_facetgrid.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 """
 ==================================
 Multiple plots and map projections

doc/gallery/plot_colorbar_center.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 """
 ==================
 Centered colormaps

doc/gallery/plot_control_colorbar.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 """
 ===========================
 Control the plot's colorbar

doc/gallery/plot_lines_from_2d.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 """
 ==================================
 Multiple lines from a 2d DataArray

doc/gallery/plot_rasterio.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 """
 .. _recipes.rasterio:
 

doc/gallery/plot_rasterio_rgb.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 """
 .. _recipes.rasterio_rgb:
 

xarray/_version.py

@@ -94,7 +94,7 @@ def run_command(commands, args, cwd=None, verbose=False, hide_stderr=False, env=
             return None, None
     else:
         if verbose:
-            print("unable to find command, tried %s" % (commands,))
+            print(f"unable to find command, tried {commands}")
         return None, None
     stdout = p.communicate()[0].strip()
     if sys.version_info[0] >= 3:
@@ -302,9 +302,8 @@ def git_pieces_from_vcs(tag_prefix, root, verbose, run_command=run_command):
             if verbose:
                 fmt = "tag '%s' doesn't start with prefix '%s'"
                 print(fmt % (full_tag, tag_prefix))
-            pieces["error"] = "tag '%s' doesn't start with prefix '%s'" % (
-                full_tag,
-                tag_prefix,
+            pieces["error"] = "tag '{}' doesn't start with prefix '{}'".format(
+                full_tag, tag_prefix
             )
             return pieces
         pieces["closest-tag"] = full_tag[len(tag_prefix) :]

xarray/backends/api.py

@@ -718,7 +718,7 @@ def open_mfdataset(
     autoclose=None,
     parallel=False,
     join="outer",
-    **kwargs
+    **kwargs,
 ):
     """Open multiple files as a single dataset.
 
@@ -1258,9 +1258,7 @@ def _validate_append_dim_and_encoding(
         return
     if append_dim:
         if append_dim not in ds.dims:
-            raise ValueError(
-                "{} not a valid dimension in the Dataset".format(append_dim)
-            )
+            raise ValueError(f"{append_dim} not a valid dimension in the Dataset")
     for data_var in ds_to_append:
         if data_var in ds:
             if append_dim is None:

xarray/backends/file_manager.py

@@ -83,7 +83,7 @@ def __init__(
         kwargs=None,
         lock=None,
         cache=None,
-        ref_counts=None
+        ref_counts=None,
     ):
         """Initialize a FileManager.
 
@@ -267,7 +267,7 @@ def __setstate__(self, state):
     def __repr__(self):
         args_string = ", ".join(map(repr, self._args))
         if self._mode is not _DEFAULT_MODE:
-            args_string += ", mode={!r}".format(self._mode)
+            args_string += f", mode={self._mode!r}"
         return "{}({!r}, {}, kwargs={})".format(
             type(self).__name__, self._opener, args_string, self._kwargs
         )

xarray/backends/netCDF4_.py

@@ -137,7 +137,7 @@ def _nc4_dtype(var):
     elif var.dtype.kind in ["i", "u", "f", "c", "S"]:
         dtype = var.dtype
     else:
-        raise ValueError("unsupported dtype for netCDF4 variable: {}".format(var.dtype))
+        raise ValueError(f"unsupported dtype for netCDF4 variable: {var.dtype}")
     return dtype
 
 

xarray/backends/netcdf3.py

@@ -50,7 +50,7 @@ def coerce_nc3_dtype(arr):
         cast_arr = arr.astype(new_dtype)
         if not (cast_arr == arr).all():
             raise ValueError(
-                "could not safely cast array from dtype %s to %s" % (dtype, new_dtype)
+                f"could not safely cast array from dtype {dtype} to {new_dtype}"
             )
         arr = cast_arr
     return arr

xarray/backends/pydap_.py

@@ -49,7 +49,7 @@ def _fix_attributes(attributes):
             # dot-separated key
             attributes.update(
                 {
-                    "{}.{}".format(k, k_child): v_child
+                    f"{k}.{k_child}": v_child
                     for k_child, v_child in attributes.pop(k).items()
                 }
             )

xarray/coding/cftime_offsets.py

@@ -638,7 +638,7 @@ def __apply__(self, other):
 
 
 _FREQUENCY_CONDITION = "|".join(_FREQUENCIES.keys())
-_PATTERN = r"^((?P<multiple>\d+)|())(?P<freq>({}))$".format(_FREQUENCY_CONDITION)
+_PATTERN = fr"^((?P<multiple>\d+)|())(?P<freq>({_FREQUENCY_CONDITION}))$"
 
 
 # pandas defines these offsets as "Tick" objects, which for instance have
@@ -759,19 +759,15 @@ def _generate_range(start, end, periods, offset):
 
             next_date = current + offset
             if next_date <= current:
-                raise ValueError(
-                    "Offset {offset} did not increment date".format(offset=offset)
-                )
+                raise ValueError(f"Offset {offset} did not increment date")
             current = next_date
     else:
         while current >= end:
             yield current
 
             next_date = current + offset
             if next_date >= current:
-                raise ValueError(
-                    "Offset {offset} did not decrement date".format(offset=offset)
-                )
+                raise ValueError(f"Offset {offset} did not decrement date")
             current = next_date
 
 

xarray/coding/cftimeindex.py

@@ -403,7 +403,7 @@ def shift(self, n, freq):
         from .cftime_offsets import to_offset
 
         if not isinstance(n, int):
-            raise TypeError("'n' must be an int, got {}.".format(n))
+            raise TypeError(f"'n' must be an int, got {n}.")
         if isinstance(freq, timedelta):
             return self + n * freq
         elif isinstance(freq, str):

xarray/coding/strings.py

@@ -228,7 +228,7 @@ def shape(self):
         return self.array.shape[:-1]
 
     def __repr__(self):
-        return "%s(%r)" % (type(self).__name__, self.array)
+        return "{}({!r})".format(type(self).__name__, self.array)
 
     def __getitem__(self, key):
         # require slicing the last dimension completely

xarray/coding/times.py

@@ -286,7 +286,7 @@ def infer_datetime_units(dates):
         # NumPy casting bug: https://github.com/numpy/numpy/issues/11096
         unique_timedeltas = to_timedelta_unboxed(unique_timedeltas)
     units = _infer_time_units_from_diff(unique_timedeltas)
-    return "%s since %s" % (units, reference_date)
+    return f"{units} since {reference_date}"
 
 
 def format_cftime_datetime(date):
@@ -341,7 +341,7 @@ def cftime_to_nptime(times):
 def _cleanup_netcdf_time_units(units):
     delta, ref_date = _unpack_netcdf_time_units(units)
     try:
-        units = "%s since %s" % (delta, format_timestamp(ref_date))
+        units = "{} since {}".format(delta, format_timestamp(ref_date))
     except OutOfBoundsDatetime:
         # don't worry about reifying the units if they're out of bounds
         pass

xarray/coding/variables.py

@@ -73,11 +73,8 @@ def __array__(self, dtype=None):
         return self.func(self.array)
 
     def __repr__(self):
-        return "%s(%r, func=%r, dtype=%r)" % (
-            type(self).__name__,
-            self.array,
-            self.func,
-            self.dtype,
+        return "{}({!r}, func={!r}, dtype={!r})".format(
+            type(self).__name__, self.array, self.func, self.dtype
         )
 
 
@@ -113,7 +110,7 @@ def unpack_for_decoding(var):
 
 def safe_setitem(dest, key, value, name=None):
     if key in dest:
-        var_str = " on variable {!r}".format(name) if name else ""
+        var_str = f" on variable {name!r}" if name else ""
         raise ValueError(
             "failed to prevent overwriting existing key {} in attrs{}. "
             "This is probably an encoding field used by xarray to describe "

xarray/convert.py

@@ -229,16 +229,14 @@ def _iris_cell_methods_to_str(cell_methods_obj):
     """
     cell_methods = []
     for cell_method in cell_methods_obj:
-        names = "".join(["{}: ".format(n) for n in cell_method.coord_names])
+        names = "".join([f"{n}: " for n in cell_method.coord_names])
         intervals = " ".join(
-            ["interval: {}".format(interval) for interval in cell_method.intervals]
-        )
-        comments = " ".join(
-            ["comment: {}".format(comment) for comment in cell_method.comments]
+            [f"interval: {interval}" for interval in cell_method.intervals]
         )
+        comments = " ".join([f"comment: {comment}" for comment in cell_method.comments])
         extra = " ".join([intervals, comments]).strip()
         if extra:
-            extra = " ({})".format(extra)
+            extra = f" ({extra})"
         cell_methods.append(names + cell_method.method + extra)
     return " ".join(cell_methods)
 
@@ -267,11 +265,11 @@ def from_iris(cube):
             dim_coord = cube.coord(dim_coords=True, dimensions=(i,))
             dims.append(_name(dim_coord))
         except iris.exceptions.CoordinateNotFoundError:
-            dims.append("dim_{}".format(i))
+            dims.append(f"dim_{i}")
 
     if len(set(dims)) != len(dims):
         duplicates = [k for k, v in Counter(dims).items() if v > 1]
-        raise ValueError("Duplicate coordinate name {}.".format(duplicates))
+        raise ValueError(f"Duplicate coordinate name {duplicates}.")
 
     coords = {}
 

xarray/core/alignment.py

@@ -64,7 +64,7 @@ def align(
     copy=True,
     indexes=None,
     exclude=frozenset(),
-    fill_value=dtypes.NA
+    fill_value=dtypes.NA,
 ):
     """
     Given any number of Dataset and/or DataArray objects, returns new
@@ -294,9 +294,7 @@ def align(
                 or dim in unlabeled_dim_sizes
             ):
                 if join == "exact":
-                    raise ValueError(
-                        "indexes along dimension {!r} are not equal".format(dim)
-                    )
+                    raise ValueError(f"indexes along dimension {dim!r} are not equal")
                 index = joiner(matching_indexes)
                 joined_indexes[dim] = index
             else:
@@ -402,7 +400,7 @@ def is_alignable(obj):
         copy=copy,
         indexes=indexes,
         exclude=exclude,
-        fill_value=fill_value
+        fill_value=fill_value,
     )
 
     for position, key, aligned_obj in zip(positions, keys, aligned):

xarray/core/common.py

@@ -87,7 +87,7 @@ def wrapped_func(self, dim=None, skipna=None, **kwargs):
                     skipna=skipna,
                     numeric_only=numeric_only,
                     allow_lazy=True,
-                    **kwargs
+                    **kwargs,
                 )
 
         else:
@@ -167,7 +167,7 @@ def _get_axis_num(self: Any, dim: Hashable) -> int:
         try:
             return self.dims.index(dim)
         except ValueError:
-            raise ValueError("%r not found in array dimensions %r" % (dim, self.dims))
+            raise ValueError(f"{dim!r} not found in array dimensions {self.dims!r}")
 
     @property
     def sizes(self: Any) -> Mapping[Hashable, int]:
@@ -225,7 +225,7 @@ def __getattr__(self, name: str) -> Any:
                 with suppress(KeyError):
                     return source[name]
         raise AttributeError(
-            "%r object has no attribute %r" % (type(self).__name__, name)
+            "{!r} object has no attribute {!r}".format(type(self).__name__, name)
         )
 
     # This complicated two-method design boosts overall performance of simple operations
@@ -258,7 +258,9 @@ def __setattr__(self, name: str, value: Any) -> None:
         except AttributeError as e:
             # Don't accidentally shadow custom AttributeErrors, e.g.
             # DataArray.dims.setter
-            if str(e) != "%r object has no attribute %r" % (type(self).__name__, name):
+            if str(e) != "{!r} object has no attribute {!r}".format(
+                type(self).__name__, name
+            ):
                 raise
             raise AttributeError(
                 "cannot set attribute %r on a %r object. Use __setitem__ style"
@@ -479,7 +481,7 @@ def pipe(
         self,
         func: Union[Callable[..., T], Tuple[Callable[..., T], str]],
         *args,
-        **kwargs
+        **kwargs,
     ) -> T:
         """
         Apply func(self, *args, **kwargs)
@@ -735,7 +737,7 @@ def rolling(
         dim: Mapping[Hashable, int] = None,
         min_periods: int = None,
         center: bool = False,
-        **window_kwargs: int
+        **window_kwargs: int,
     ):
         """
         Rolling window object.
@@ -799,7 +801,7 @@ def rolling_exp(
         self,
         window: Mapping[Hashable, int] = None,
         window_type: str = "span",
-        **window_kwargs
+        **window_kwargs,
     ):
         """
         Exponentially-weighted moving window.
@@ -840,7 +842,7 @@ def coarsen(
         boundary: str = "exact",
         side: Union[str, Mapping[Hashable, str]] = "left",
         coord_func: str = "mean",
-        **window_kwargs: int
+        **window_kwargs: int,
     ):
         """
         Coarsen object.
@@ -910,7 +912,7 @@ def resample(
         keep_attrs: bool = None,
         loffset=None,
         restore_coord_dims: bool = None,
-        **indexer_kwargs: str
+        **indexer_kwargs: str,
     ):
         """Returns a Resample object for performing resampling operations.