minor lint tweaks (#3429)

* pyflakes 2.1.1 and f-strings

* Tweaks from mypy 0.740 (will skip to 0.750: mypy#7735)

* black -t py36

* isort

* fix tests

xarray/backends/h5netcdf_.py

@@ -245,7 +245,7 @@ def prepare_variable(
                 dtype=dtype,
                 dimensions=variable.dims,
                 fillvalue=fillvalue,
-                **kwargs
+                **kwargs,
             )
         else:
             nc4_var = self.ds[name]

xarray/backends/zarr.py

@@ -467,7 +467,7 @@ def open_zarr(
     drop_variables=None,
     consolidated=False,
     overwrite_encoded_chunks=False,
-    **kwargs
+    **kwargs,
 ):
     """Load and decode a dataset from a Zarr store.
 

xarray/core/accessor_dt.py

@@ -178,7 +178,9 @@ def __init__(self, obj):
             )
         self._obj = obj
 
-    def _tslib_field_accessor(name, docstring=None, dtype=None):
+    def _tslib_field_accessor(  # type: ignore
+        name: str, docstring: str = None, dtype: np.dtype = None
+    ):
         def f(self, dtype=dtype):
             if dtype is None:
                 dtype = self._obj.dtype

xarray/core/arithmetic.py

@@ -76,7 +76,7 @@ def __array_ufunc__(self, ufunc, method, *inputs, **kwargs):
             dataset_join=dataset_join,
             dataset_fill_value=np.nan,
             kwargs=kwargs,
-            dask="allowed"
+            dask="allowed",
         )
 
     # this has no runtime function - these are listed so IDEs know these

xarray/core/coordinates.py

@@ -367,7 +367,7 @@ def remap_label_indexers(
     indexers: Mapping[Hashable, Any] = None,
     method: str = None,
     tolerance=None,
-    **indexers_kwargs: Any
+    **indexers_kwargs: Any,
 ) -> Tuple[dict, dict]:  # TODO more precise return type after annotations in indexing
     """Remap indexers from obj.coords.
     If indexer is an instance of DataArray and it has coordinate, then this coordinate

xarray/core/dataset.py

@@ -2967,15 +2967,13 @@ def expand_dims(
                     for a in axis:
                         if a < -result_ndim or result_ndim - 1 < a:
                             raise IndexError(
-                                "Axis {a} is out of bounds of the expanded"
-                                " dimension size {dim}.".format(
-                                    a=a, v=k, dim=result_ndim
-                                )
+                                f"Axis {a} of variable {k} is out of bounds of the "
+                                f"expanded dimension size {result_ndim}"
                             )
 
                     axis_pos = [a if a >= 0 else result_ndim + a for a in axis]
                     if len(axis_pos) != len(set(axis_pos)):
-                        raise ValueError("axis should not contain duplicate" " values.")
+                        raise ValueError("axis should not contain duplicate values")
                     # We need to sort them to make sure `axis` equals to the
                     # axis positions of the result array.
                     zip_axis_dim = sorted(zip(axis_pos, dim.items()))
@@ -3131,7 +3129,7 @@ def reorder_levels(
             coord = self._variables[dim]
             index = self.indexes[dim]
             if not isinstance(index, pd.MultiIndex):
-                raise ValueError("coordinate %r has no MultiIndex" % dim)
+                raise ValueError(f"coordinate {dim} has no MultiIndex")
             new_index = index.reorder_levels(order)
             variables[dim] = IndexVariable(coord.dims, new_index)
             indexes[dim] = new_index

xarray/core/indexing.py

@@ -59,8 +59,7 @@ def _sanitize_slice_element(x):
     if isinstance(x, np.ndarray):
         if x.ndim != 0:
             raise ValueError(
-                "cannot use non-scalar arrays in a slice for "
-                "xarray indexing: {}".format(x)
+                f"cannot use non-scalar arrays in a slice for xarray indexing: {x}"
             )
         x = x[()]
 
@@ -128,9 +127,9 @@ def convert_label_indexer(index, label, index_name="", method=None, tolerance=No
             # unlike pandas, in xarray we never want to silently convert a
             # slice indexer into an array indexer
             raise KeyError(
-                "cannot represent labeled-based slice indexer for "
-                "dimension %r with a slice over integer positions; "
-                "the index is unsorted or non-unique" % index_name
+                "cannot represent labeled-based slice indexer for dimension "
+                f"{index_name!r} with a slice over integer positions; the index is "
+                "unsorted or non-unique"
             )
 
     elif is_dict_like(label):
@@ -190,7 +189,7 @@ def convert_label_indexer(index, label, index_name="", method=None, tolerance=No
                 )
             indexer = get_indexer_nd(index, label, method, tolerance)
             if np.any(indexer < 0):
-                raise KeyError("not all values found in index %r" % index_name)
+                raise KeyError(f"not all values found in index {index_name!r}")
     return indexer, new_index
 
 
@@ -208,7 +207,7 @@ def get_dim_indexers(data_obj, indexers):
         if k not in data_obj.dims and k not in data_obj._level_coords
     ]
     if invalid:
-        raise ValueError("dimensions or multi-index levels %r do not exist" % invalid)
+        raise ValueError(f"dimensions or multi-index levels {invalid!r} do not exist")
 
     level_indexers = defaultdict(dict)
     dim_indexers = {}
@@ -223,8 +222,8 @@ def get_dim_indexers(data_obj, indexers):
     for dim, level_labels in level_indexers.items():
         if dim_indexers.get(dim, False):
             raise ValueError(
-                "cannot combine multi-index level indexers "
-                "with an indexer for dimension %s" % dim
+                "cannot combine multi-index level indexers with an indexer for "
+                f"dimension {dim}"
             )
         dim_indexers[dim] = level_labels
 
@@ -326,7 +325,7 @@ def tuple(self):
         return self._key
 
     def __repr__(self):
-        return "{}({})".format(type(self).__name__, self.tuple)
+        return f"{type(self).__name__}({self.tuple})"
 
 
 def as_integer_or_none(value):
@@ -362,9 +361,7 @@ def __init__(self, key):
                 k = as_integer_slice(k)
             else:
                 raise TypeError(
-                    "unexpected indexer type for {}: {!r}".format(
-                        type(self).__name__, k
-                    )
+                    f"unexpected indexer type for {type(self).__name__}: {k!r}"
                 )
             new_key.append(k)
 
@@ -395,20 +392,17 @@ def __init__(self, key):
             elif isinstance(k, np.ndarray):
                 if not np.issubdtype(k.dtype, np.integer):
                     raise TypeError(
-                        "invalid indexer array, does not have "
-                        "integer dtype: {!r}".format(k)
+                        f"invalid indexer array, does not have integer dtype: {k!r}"
                     )
                 if k.ndim != 1:
                     raise TypeError(
-                        "invalid indexer array for {}, must have "
-                        "exactly 1 dimension: ".format(type(self).__name__, k)
+                        f"invalid indexer array for {type(self).__name__}; must have "
+                        f"exactly 1 dimension: {k!r}"
                     )
                 k = np.asarray(k, dtype=np.int64)
             else:
                 raise TypeError(
-                    "unexpected indexer type for {}: {!r}".format(
-                        type(self).__name__, k
-                    )
+                    f"unexpected indexer type for {type(self).__name__}: {k!r}"
                 )
             new_key.append(k)
 
@@ -439,23 +433,20 @@ def __init__(self, key):
             elif isinstance(k, np.ndarray):
                 if not np.issubdtype(k.dtype, np.integer):
                     raise TypeError(
-                        "invalid indexer array, does not have "
-                        "integer dtype: {!r}".format(k)
+                        f"invalid indexer array, does not have integer dtype: {k!r}"
                     )
                 if ndim is None:
                     ndim = k.ndim
                 elif ndim != k.ndim:
                     ndims = [k.ndim for k in key if isinstance(k, np.ndarray)]
                     raise ValueError(
                         "invalid indexer key: ndarray arguments "
-                        "have different numbers of dimensions: {}".format(ndims)
+                        f"have different numbers of dimensions: {ndims}"
                     )
                 k = np.asarray(k, dtype=np.int64)
             else:
                 raise TypeError(
-                    "unexpected indexer type for {}: {!r}".format(
-                        type(self).__name__, k
-                    )
+                    f"unexpected indexer type for {type(self).__name__}: {k!r}"
                 )
             new_key.append(k)
 
@@ -574,9 +565,7 @@ def __setitem__(self, key, value):
         self.array[full_key] = value
 
     def __repr__(self):
-        return "{}(array={!r}, key={!r})".format(
-            type(self).__name__, self.array, self.key
-        )
+        return f"{type(self).__name__}(array={self.array!r}, key={self.key!r})"
 
 
 class LazilyVectorizedIndexedArray(ExplicitlyIndexedNDArrayMixin):
@@ -627,9 +616,7 @@ def __setitem__(self, key, value):
         )
 
     def __repr__(self):
-        return "{}(array={!r}, key={!r})".format(
-            type(self).__name__, self.array, self.key
-        )
+        return f"{type(self).__name__}(array={self.array!r}, key={self.key!r})"
 
 
 def _wrap_numpy_scalars(array):

xarray/core/missing.py

@@ -71,7 +71,7 @@ def __call__(self, x):
             self._yi,
             left=self._left,
             right=self._right,
-            **self.call_kwargs
+            **self.call_kwargs,
         )
 
 
@@ -93,7 +93,7 @@ def __init__(
         copy=False,
         bounds_error=False,
         order=None,
-        **kwargs
+        **kwargs,
     ):
         from scipy.interpolate import interp1d
 
@@ -126,7 +126,7 @@ def __init__(
             bounds_error=False,
             assume_sorted=assume_sorted,
             copy=copy,
-            **self.cons_kwargs
+            **self.cons_kwargs,
         )
 
 
@@ -147,7 +147,7 @@ def __init__(
         order=3,
         nu=0,
         ext=None,
-        **kwargs
+        **kwargs,
     ):
         from scipy.interpolate import UnivariateSpline
 

xarray/core/resample.py

@@ -151,7 +151,7 @@ def _interpolate(self, kind="linear"):
             assume_sorted=True,
             method=kind,
             kwargs={"bounds_error": False},
-            **{self._dim: self._full_index}
+            **{self._dim: self._full_index},
         )
 
 

xarray/core/rolling.py

@@ -1,4 +1,5 @@
 import functools
+from typing import Callable
 
 import numpy as np
 
@@ -106,7 +107,7 @@ def __repr__(self):
     def __len__(self):
         return self.obj.sizes[self.dim]
 
-    def _reduce_method(name):
+    def _reduce_method(name: str) -> Callable:  # type: ignore
         array_agg_func = getattr(duck_array_ops, name)
         bottleneck_move_func = getattr(bottleneck, "move_" + name, None)
 
@@ -453,7 +454,7 @@ def _numpy_or_bottleneck_reduce(
                 array_agg_func=array_agg_func,
                 bottleneck_move_func=bottleneck_move_func,
             ),
-            **kwargs
+            **kwargs,
         )
 
     def construct(self, window_dim, stride=1, fill_value=dtypes.NA):

xarray/plot/__init__.py

@@ -1,6 +1,6 @@
+from .dataset_plot import scatter
 from .facetgrid import FacetGrid
 from .plot import contour, contourf, hist, imshow, line, pcolormesh, plot, step
-from .dataset_plot import scatter
 
 __all__ = [
     "plot",

xarray/plot/facetgrid.py

@@ -294,7 +294,7 @@ def map_dataarray_line(
                     hue=hue,
                     add_legend=False,
                     _labels=False,
-                    **kwargs
+                    **kwargs,
                 )
                 self._mappables.append(mappable)
 
@@ -376,7 +376,7 @@ def add_legend(self, **kwargs):
             labels=list(self._hue_var.values),
             title=self._hue_label,
             loc="center right",
-            **kwargs
+            **kwargs,
         )
 
         self.figlegend = figlegend
@@ -491,7 +491,7 @@ def set_titles(self, template="{coord} = {value}", maxchar=30, size=None, **kwar
                     rotation=270,
                     ha="left",
                     va="center",
-                    **kwargs
+                    **kwargs,
                 )
 
             # The column titles on the top row
@@ -590,7 +590,7 @@ def _easy_facetgrid(
     subplot_kws=None,
     ax=None,
     figsize=None,
-    **kwargs
+    **kwargs,
 ):
     """
     Convenience method to call xarray.plot.FacetGrid from 2d plotting methods

xarray/tests/test_dataarray.py

@@ -1534,11 +1534,11 @@ def test_expand_dims_error(self):
             # Should not pass the already existing dimension.
             array.expand_dims(dim=["x"])
         # raise if duplicate
-        with raises_regex(ValueError, "duplicate values."):
+        with raises_regex(ValueError, "duplicate values"):
             array.expand_dims(dim=["y", "y"])
-        with raises_regex(ValueError, "duplicate values."):
+        with raises_regex(ValueError, "duplicate values"):
             array.expand_dims(dim=["y", "z"], axis=[1, 1])
-        with raises_regex(ValueError, "duplicate values."):
+        with raises_regex(ValueError, "duplicate values"):
             array.expand_dims(dim=["y", "z"], axis=[2, -2])
 
         # out of bounds error, axis must be in [-4, 3]

xarray/tutorial.py

@@ -32,7 +32,7 @@ def open_dataset(
     cache_dir=_default_cache_dir,
     github_url="https://github.com/pydata/xarray-data",
     branch="master",
-    **kws
+    **kws,
 ):
     """
     Open a dataset from the online repository (requires internet).