Merge branch 'master' into fix-issue-10244

11 files changed, 316 insertions, 80 deletions

diff --git a/numpy/ma/__init__.pyi b/numpy/ma/__init__.pyi
new file mode 100644
index 000000000..d1259abcc
--- /dev/null
+++ b/numpy/ma/__init__.pyi
@@ -0,0 +1,225 @@
+from typing import Any
+
+core: Any
+extras: Any
+MAError: Any
+MaskError: Any
+MaskType: Any
+MaskedArray: Any
+abs: Any
+absolute: Any
+add: Any
+all: Any
+allclose: Any
+allequal: Any
+alltrue: Any
+amax: Any
+amin: Any
+angle: Any
+anom: Any
+anomalies: Any
+any: Any
+append: Any
+arange: Any
+arccos: Any
+arccosh: Any
+arcsin: Any
+arcsinh: Any
+arctan: Any
+arctan2: Any
+arctanh: Any
+argmax: Any
+argmin: Any
+argsort: Any
+around: Any
+array: Any
+asanyarray: Any
+asarray: Any
+bitwise_and: Any
+bitwise_or: Any
+bitwise_xor: Any
+bool_: Any
+ceil: Any
+choose: Any
+clip: Any
+common_fill_value: Any
+compress: Any
+compressed: Any
+concatenate: Any
+conjugate: Any
+convolve: Any
+copy: Any
+correlate: Any
+cos: Any
+cosh: Any
+count: Any
+cumprod: Any
+cumsum: Any
+default_fill_value: Any
+diag: Any
+diagonal: Any
+diff: Any
+divide: Any
+empty: Any
+empty_like: Any
+equal: Any
+exp: Any
+expand_dims: Any
+fabs: Any
+filled: Any
+fix_invalid: Any
+flatten_mask: Any
+flatten_structured_array: Any
+floor: Any
+floor_divide: Any
+fmod: Any
+frombuffer: Any
+fromflex: Any
+fromfunction: Any
+getdata: Any
+getmask: Any
+getmaskarray: Any
+greater: Any
+greater_equal: Any
+harden_mask: Any
+hypot: Any
+identity: Any
+ids: Any
+indices: Any
+inner: Any
+innerproduct: Any
+isMA: Any
+isMaskedArray: Any
+is_mask: Any
+is_masked: Any
+isarray: Any
+left_shift: Any
+less: Any
+less_equal: Any
+log: Any
+log10: Any
+log2: Any
+logical_and: Any
+logical_not: Any
+logical_or: Any
+logical_xor: Any
+make_mask: Any
+make_mask_descr: Any
+make_mask_none: Any
+mask_or: Any
+masked: Any
+masked_array: Any
+masked_equal: Any
+masked_greater: Any
+masked_greater_equal: Any
+masked_inside: Any
+masked_invalid: Any
+masked_less: Any
+masked_less_equal: Any
+masked_not_equal: Any
+masked_object: Any
+masked_outside: Any
+masked_print_option: Any
+masked_singleton: Any
+masked_values: Any
+masked_where: Any
+max: Any
+maximum: Any
+maximum_fill_value: Any
+mean: Any
+min: Any
+minimum: Any
+minimum_fill_value: Any
+mod: Any
+multiply: Any
+mvoid: Any
+ndim: Any
+negative: Any
+nomask: Any
+nonzero: Any
+not_equal: Any
+ones: Any
+outer: Any
+outerproduct: Any
+power: Any
+prod: Any
+product: Any
+ptp: Any
+put: Any
+putmask: Any
+ravel: Any
+remainder: Any
+repeat: Any
+reshape: Any
+resize: Any
+right_shift: Any
+round: Any
+round_: Any
+set_fill_value: Any
+shape: Any
+sin: Any
+sinh: Any
+size: Any
+soften_mask: Any
+sometrue: Any
+sort: Any
+sqrt: Any
+squeeze: Any
+std: Any
+subtract: Any
+sum: Any
+swapaxes: Any
+take: Any
+tan: Any
+tanh: Any
+trace: Any
+transpose: Any
+true_divide: Any
+var: Any
+where: Any
+zeros: Any
+apply_along_axis: Any
+apply_over_axes: Any
+atleast_1d: Any
+atleast_2d: Any
+atleast_3d: Any
+average: Any
+clump_masked: Any
+clump_unmasked: Any
+column_stack: Any
+compress_cols: Any
+compress_nd: Any
+compress_rowcols: Any
+compress_rows: Any
+count_masked: Any
+corrcoef: Any
+cov: Any
+diagflat: Any
+dot: Any
+dstack: Any
+ediff1d: Any
+flatnotmasked_contiguous: Any
+flatnotmasked_edges: Any
+hsplit: Any
+hstack: Any
+isin: Any
+in1d: Any
+intersect1d: Any
+mask_cols: Any
+mask_rowcols: Any
+mask_rows: Any
+masked_all: Any
+masked_all_like: Any
+median: Any
+mr_: Any
+notmasked_contiguous: Any
+notmasked_edges: Any
+polyfit: Any
+row_stack: Any
+setdiff1d: Any
+setxor1d: Any
+stack: Any
+unique: Any
+union1d: Any
+vander: Any
+vstack: Any
diff --git a/numpy/ma/bench.py b/numpy/ma/bench.py
index 83cc6aea7..e29d54365 100644
--- a/numpy/ma/bench.py
+++ b/numpy/ma/bench.py
@@ -58,7 +58,7 @@ def compare_functions_1v(func, nloop=500,
                        xs=xs, nmxs=nmxs, xl=xl, nmxl=nmxl):
     funcname = func.__name__
     print("-"*50)
-    print("%s on small arrays" % funcname)
+    print(f'{funcname} on small arrays')
     module, data = "numpy.ma", "nmxs"
     timer("%(module)s.%(funcname)s(%(data)s)" % locals(), v="%11s" % module, nloop=nloop)
 
@@ -70,8 +70,8 @@ def compare_functions_1v(func, nloop=500,
 def compare_methods(methodname, args, vars='x', nloop=500, test=True,
                     xs=xs, nmxs=nmxs, xl=xl, nmxl=nmxl):
     print("-"*50)
-    print("%s on small arrays" % methodname)
-    data, ver = "nm%ss" % vars, 'numpy.ma'
+    print(f'{methodname} on small arrays')
+    data, ver = f'nm{vars}l', 'numpy.ma'
     timer("%(data)s.%(methodname)s(%(args)s)" % locals(), v=ver, nloop=nloop)
 
     print("%s on large arrays" % methodname)
@@ -86,11 +86,11 @@ def compare_functions_2v(func, nloop=500, test=True,
                        yl=yl, nmyl=nmyl):
     funcname = func.__name__
     print("-"*50)
-    print("%s on small arrays" % funcname)
+    print(f'{funcname} on small arrays')
     module, data = "numpy.ma", "nmxs,nmys"
     timer("%(module)s.%(funcname)s(%(data)s)" % locals(), v="%11s" % module, nloop=nloop)
 
-    print("%s on large arrays" % funcname)
+    print(f'{funcname} on large arrays')
     module, data = "numpy.ma", "nmxl,nmyl"
     timer("%(module)s.%(funcname)s(%(data)s)" % locals(), v="%11s" % module, nloop=nloop)
     return
diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index b5371f51a..d6af22337 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -443,9 +443,9 @@ def _check_fill_value(fill_value, ndtype):
         if isinstance(fill_value, (ndarray, np.void)):
             try:
                 fill_value = np.array(fill_value, copy=False, dtype=ndtype)
-            except ValueError:
+            except ValueError as e:
                 err_msg = "Unable to transform %s to dtype %s"
-                raise ValueError(err_msg % (fill_value, ndtype))
+                raise ValueError(err_msg % (fill_value, ndtype)) from e
         else:
             fill_value = np.asarray(fill_value, dtype=object)
             fill_value = np.array(_recursive_set_fill_value(fill_value, ndtype),
@@ -460,12 +460,12 @@ def _check_fill_value(fill_value, ndtype):
             # Also in case of converting string arrays.
             try:
                 fill_value = np.array(fill_value, copy=False, dtype=ndtype)
-            except (OverflowError, ValueError):
+            except (OverflowError, ValueError) as e:
                 # Raise TypeError instead of OverflowError or ValueError.
                 # OverflowError is seldom used, and the real problem here is
                 # that the passed fill_value is not compatible with the ndtype.
                 err_msg = "Cannot convert fill_value %s to dtype %s"
-                raise TypeError(err_msg % (fill_value, ndtype))
+                raise TypeError(err_msg % (fill_value, ndtype)) from e
     return np.array(fill_value)
 
 
@@ -1489,7 +1489,7 @@ def is_mask(m):
 
     See Also
     --------
-    isMaskedArray : Test whether input is an instance of MaskedArray.
+    ma.isMaskedArray : Test whether input is an instance of MaskedArray.
 
     Examples
     --------
@@ -2812,7 +2812,7 @@ class MaskedArray(ndarray):
 
     def __new__(cls, data=None, mask=nomask, dtype=None, copy=False,
                 subok=True, ndmin=0, fill_value=None, keep_mask=True,
-                hard_mask=None, shrink=True, order=None, **options):
+                hard_mask=None, shrink=True, order=None):
         """
         Create a new masked array from scratch.
 
@@ -3538,11 +3538,12 @@ class MaskedArray(ndarray):
         Force the mask to hard.
 
         Whether the mask of a masked array is hard or soft is determined by
-        its `hardmask` property. `harden_mask` sets `hardmask` to True.
+        its `~ma.MaskedArray.hardmask` property. `harden_mask` sets
+        `~ma.MaskedArray.hardmask` to ``True``.
 
         See Also
         --------
-        hardmask
+        ma.MaskedArray.hardmask
 
         """
         self._hardmask = True
@@ -3553,11 +3554,12 @@ class MaskedArray(ndarray):
         Force the mask to soft.
 
         Whether the mask of a masked array is hard or soft is determined by
-        its `hardmask` property. `soften_mask` sets `hardmask` to False.
+        its `~ma.MaskedArray.hardmask` property. `soften_mask` sets
+        `~ma.MaskedArray.hardmask` to ``False``.
 
         See Also
         --------
-        hardmask
+        ma.MaskedArray.hardmask
 
         """
         self._hardmask = False
@@ -3832,7 +3834,7 @@ class MaskedArray(ndarray):
         """
         Return `a` where condition is ``True``.
 
-        If condition is a `MaskedArray`, missing values are considered
+        If condition is a `~ma.MaskedArray`, missing values are considered
         as ``False``.
 
         Parameters
@@ -3851,7 +3853,7 @@ class MaskedArray(ndarray):
         Returns
         -------
         result : MaskedArray
-            A :class:`MaskedArray` object.
+            A :class:`~ma.MaskedArray` object.
 
         Notes
         -----
@@ -4461,7 +4463,7 @@ class MaskedArray(ndarray):
 
         See Also
         --------
-        count_masked : Count masked elements in array or along a given axis.
+        ma.count_masked : Count masked elements in array or along a given axis.
 
         Examples
         --------
@@ -5103,7 +5105,7 @@ class MaskedArray(ndarray):
 
         Notes
         -----
-        The mask is lost if `out` is not a valid :class:`MaskedArray` !
+        The mask is lost if `out` is not a valid :class:`ma.MaskedArray` !
 
         Arithmetic is modular when using integer types, and no error is
         raised on overflow.
@@ -5389,7 +5391,7 @@ class MaskedArray(ndarray):
 
         See Also
         --------
-        numpy.ndarray.around : corresponding function for ndarrays
+        numpy.ndarray.round : corresponding function for ndarrays
         numpy.around : equivalent function
         """
         result = self._data.round(decimals=decimals, out=out).view(type(self))
@@ -5437,7 +5439,7 @@ class MaskedArray(ndarray):
             When the array contains unmasked values at the same extremes of the
             datatype, the ordering of these values and the masked values is
             undefined.
-        fill_value : {var}, optional
+        fill_value : scalar or None, optional
             Value used internally for the masked values.
             If ``fill_value`` is not None, it supersedes ``endwith``.
 
@@ -5449,7 +5451,7 @@ class MaskedArray(ndarray):
 
         See Also
         --------
-        MaskedArray.sort : Describes sorting algorithms used.
+        ma.MaskedArray.sort : Describes sorting algorithms used.
         lexsort : Indirect stable sort with multiple keys.
         numpy.ndarray.sort : Inplace sort.
 
@@ -5495,7 +5497,7 @@ class MaskedArray(ndarray):
         axis : {None, integer}
             If None, the index is into the flattened array, otherwise along
             the specified axis
-        fill_value : {var}, optional
+        fill_value : scalar or None, optional
             Value used to fill in the masked values.  If None, the output of
             minimum_fill_value(self._data) is used instead.
         out : {None, array}, optional
@@ -5541,7 +5543,7 @@ class MaskedArray(ndarray):
         axis : {None, integer}
             If None, the index is into the flattened array, otherwise along
             the specified axis
-        fill_value : {var}, optional
+        fill_value : scalar or None, optional
             Value used to fill in the masked values.  If None, the output of
             maximum_fill_value(self._data) is used instead.
         out : {None, array}, optional
@@ -5592,7 +5594,7 @@ class MaskedArray(ndarray):
             When the array contains unmasked values sorting at the same extremes of the
             datatype, the ordering of these values and the masked values is
             undefined.
-        fill_value : {var}, optional
+        fill_value : scalar or None, optional
             Value used internally for the masked values.
             If ``fill_value`` is not None, it supersedes ``endwith``.
 
@@ -5663,7 +5665,7 @@ class MaskedArray(ndarray):
         out : array_like, optional
             Alternative output array in which to place the result.  Must be of
             the same shape and buffer length as the expected output.
-        fill_value : {var}, optional
+        fill_value : scalar or None, optional
             Value used to fill in the masked values.
             If None, use the output of `minimum_fill_value`.
         keepdims : bool, optional
@@ -5679,7 +5681,7 @@ class MaskedArray(ndarray):
 
         See Also
         --------
-        minimum_fill_value
+        ma.minimum_fill_value
             Returns the minimum filling value for a given datatype.
 
         """
@@ -5797,7 +5799,7 @@ class MaskedArray(ndarray):
         out : array_like, optional
             Alternative output array in which to place the result.  Must
             be of the same shape and buffer length as the expected output.
-        fill_value : {var}, optional
+        fill_value : scalar or None, optional
             Value used to fill in the masked values.
             If None, use the output of maximum_fill_value().
         keepdims : bool, optional
@@ -5813,7 +5815,7 @@ class MaskedArray(ndarray):
 
         See Also
         --------
-        maximum_fill_value
+        ma.maximum_fill_value
             Returns the maximum filling value for a given datatype.
 
         """
@@ -5874,7 +5876,7 @@ class MaskedArray(ndarray):
             Alternative output array in which to place the result. It must
             have the same shape and buffer length as the expected output
             but the type will be cast if necessary.
-        fill_value : {var}, optional
+        fill_value : scalar or None, optional
             Value used to fill in the masked values.
         keepdims : bool, optional
             If this is set to True, the axes which are reduced are left
@@ -6907,11 +6909,11 @@ def compressed(x):
     Return all the non-masked data as a 1-D array.
 
     This function is equivalent to calling the "compressed" method of a
-    `MaskedArray`, see `MaskedArray.compressed` for details.
+    `ma.MaskedArray`, see `ma.MaskedArray.compressed` for details.
 
     See Also
     --------
-    MaskedArray.compressed
+    ma.MaskedArray.compressed
         Equivalent method.
 
     """
diff --git a/numpy/ma/extras.py b/numpy/ma/extras.py
index 8ede29da1..1bf03e966 100644
--- a/numpy/ma/extras.py
+++ b/numpy/ma/extras.py
@@ -901,11 +901,11 @@ def compress_rows(a):
     Suppress whole rows of a 2-D array that contain masked values.
 
     This is equivalent to ``np.ma.compress_rowcols(a, 0)``, see
-    `extras.compress_rowcols` for details.
+    `compress_rowcols` for details.
 
     See Also
     --------
-    extras.compress_rowcols
+    compress_rowcols
 
     """
     a = asarray(a)
@@ -918,11 +918,11 @@ def compress_cols(a):
     Suppress whole columns of a 2-D array that contain masked values.
 
     This is equivalent to ``np.ma.compress_rowcols(a, 1)``, see
-    `extras.compress_rowcols` for details.
+    `compress_rowcols` for details.
 
     See Also
     --------
-    extras.compress_rowcols
+    compress_rowcols
 
     """
     a = asarray(a)
@@ -1641,7 +1641,7 @@ def flatnotmasked_contiguous(a):
     slice_list : list
         A sorted sequence of `slice` objects (start index, end index).
 
-        ..versionchanged:: 1.15.0
+        .. versionchanged:: 1.15.0
             Now returns an empty list instead of None for a fully masked array
 
     See Also
diff --git a/numpy/ma/mrecords.py b/numpy/ma/mrecords.py
index cd93a9a14..70087632e 100644
--- a/numpy/ma/mrecords.py
+++ b/numpy/ma/mrecords.py
@@ -60,7 +60,7 @@ def _checknames(descr, names=None):
         elif isinstance(names, str):
             new_names = names.split(',')
         else:
-            raise NameError("illegal input names %s" % repr(names))
+            raise NameError(f'illegal input names {names!r}')
         nnames = len(new_names)
         if nnames < ndescr:
             new_names += default_names[nnames:]
@@ -198,8 +198,8 @@ class MaskedRecords(MaskedArray):
         fielddict = ndarray.__getattribute__(self, 'dtype').fields
         try:
             res = fielddict[attr][:2]
-        except (TypeError, KeyError):
-            raise AttributeError("record array has no attribute %s" % attr)
+        except (TypeError, KeyError) as e:
+            raise AttributeError(f'record array has no attribute {attr}') from e
         # So far, so good
         _localdict = ndarray.__getattribute__(self, '__dict__')
         _data = ndarray.view(self, _localdict['_baseclass'])
@@ -274,7 +274,7 @@ class MaskedRecords(MaskedArray):
         try:
             res = fielddict[attr][:2]
         except (TypeError, KeyError):
-            raise AttributeError("record array has no attribute %s" % attr)
+            raise AttributeError(f'record array has no attribute {attr}')
 
         if val is masked:
             _fill_value = _localdict['_fill_value']
@@ -337,13 +337,13 @@ class MaskedRecords(MaskedArray):
 
         """
         if self.size > 1:
-            mstr = ["(%s)" % ",".join([str(i) for i in s])
+            mstr = [f"({','.join([str(i) for i in s])})"
                     for s in zip(*[getattr(self, f) for f in self.dtype.names])]
-            return "[%s]" % ", ".join(mstr)
+            return f"[{', '.join(mstr)}]"
         else:
-            mstr = ["%s" % ",".join([str(i) for i in s])
+            mstr = [f"{','.join([str(i) for i in s])}"
                     for s in zip([getattr(self, f) for f in self.dtype.names])]
-            return "(%s)" % ", ".join(mstr)
+            return f"({', '.join(mstr)})"
 
     def __repr__(self):
         """
@@ -657,7 +657,7 @@ def openfile(fname):
     try:
         f = open(fname)
     except IOError:
-        raise IOError("No such file: '%s'" % fname)
+        raise IOError(f"No such file: '{fname}'")
     if f.readline()[:2] != "\\x":
         f.seek(0, 0)
         return f
diff --git a/numpy/ma/setup.py b/numpy/ma/setup.py
index d3f34c874..018d38cdd 100644
--- a/numpy/ma/setup.py
+++ b/numpy/ma/setup.py
@@ -3,6 +3,7 @@ def configuration(parent_package='',top_path=None):
     from numpy.distutils.misc_util import Configuration
     config = Configuration('ma', parent_package, top_path)
     config.add_subpackage('tests')
+    config.add_data_files('*.pyi')
     return config
 
 if __name__ == "__main__":
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index 27f14a5e7..0b2e7303c 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -244,6 +244,10 @@ class TestMaskedArray:
                                         'offsets':[0,8]})
         array(x)  # used to fail due to 'V' padding field in x.dtype.descr
 
+    def test_unknown_keyword_parameter(self):
+        with pytest.raises(TypeError, match="unexpected keyword argument"):
+            MaskedArray([1, 2, 3], maks=[0, 1, 0])  # `mask` is misspelled.
+
     def test_asarray(self):
         (x, y, a10, m1, m2, xm, ym, z, zm, xf) = self.d
         xm.fill_value = -9999
@@ -2748,7 +2752,7 @@ class TestMaskedArrayInPlaceArithmetics:
                 xm += t(1)
                 assert_equal(xm, y + t(1))
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
     def test_inplace_addition_array_type(self):
         # Test of inplace additions
@@ -2765,7 +2769,7 @@ class TestMaskedArrayInPlaceArithmetics:
                 assert_equal(xm, y + a)
                 assert_equal(xm.mask, mask_or(m, a.mask))
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
     def test_inplace_subtraction_scalar_type(self):
         # Test of inplace subtractions
@@ -2778,7 +2782,7 @@ class TestMaskedArrayInPlaceArithmetics:
                 xm -= t(1)
                 assert_equal(xm, y - t(1))
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
     def test_inplace_subtraction_array_type(self):
         # Test of inplace subtractions
@@ -2795,7 +2799,7 @@ class TestMaskedArrayInPlaceArithmetics:
                 assert_equal(xm, y - a)
                 assert_equal(xm.mask, mask_or(m, a.mask))
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
     def test_inplace_multiplication_scalar_type(self):
         # Test of inplace multiplication
@@ -2808,7 +2812,7 @@ class TestMaskedArrayInPlaceArithmetics:
                 xm *= t(2)
                 assert_equal(xm, y * t(2))
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
     def test_inplace_multiplication_array_type(self):
         # Test of inplace multiplication
@@ -2825,7 +2829,7 @@ class TestMaskedArrayInPlaceArithmetics:
                 assert_equal(xm, y * a)
                 assert_equal(xm.mask, mask_or(m, a.mask))
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
     def test_inplace_floor_division_scalar_type(self):
         # Test of inplace division
@@ -2861,7 +2865,7 @@ class TestMaskedArrayInPlaceArithmetics:
                     mask_or(mask_or(m, a.mask), (a == t(0)))
                 )
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
     def test_inplace_division_scalar_type(self):
         # Test of inplace division
@@ -2895,9 +2899,9 @@ class TestMaskedArrayInPlaceArithmetics:
                     warnings.warn(str(e), stacklevel=1)
 
                 if issubclass(t, np.integer):
-                    assert_equal(len(sup.log), 2, "Failed on type=%s." % t)
+                    assert_equal(len(sup.log), 2, f'Failed on type={t}.')
                 else:
-                    assert_equal(len(sup.log), 0, "Failed on type=%s." % t)
+                    assert_equal(len(sup.log), 0, f'Failed on type={t}.')
 
     def test_inplace_division_array_type(self):
         # Test of inplace division
@@ -2934,9 +2938,9 @@ class TestMaskedArrayInPlaceArithmetics:
                     warnings.warn(str(e), stacklevel=1)
 
                 if issubclass(t, np.integer):
-                    assert_equal(len(sup.log), 2, "Failed on type=%s." % t)
+                    assert_equal(len(sup.log), 2, f'Failed on type={t}.')
                 else:
-                    assert_equal(len(sup.log), 0, "Failed on type=%s." % t)
+                    assert_equal(len(sup.log), 0, f'Failed on type={t}.')
 
     def test_inplace_pow_type(self):
         # Test keeping data w/ (inplace) power
@@ -2954,7 +2958,7 @@ class TestMaskedArrayInPlaceArithmetics:
                 assert_equal(x.data, xx_r.data)
                 assert_equal(x.mask, xx_r.mask)
 
-                assert_equal(len(w), 0, "Failed on type=%s." % t)
+                assert_equal(len(w), 0, f'Failed on type={t}.')
 
 
 class TestMaskedArrayMethods:
@@ -3858,8 +3862,6 @@ class TestMaskedArrayMathMethods:
             assert_almost_equal(np.sqrt(mXvar0[k]),
                                 mX[:, k].compressed().std())
 
-    @pytest.mark.skipif(sys.platform=='win32' and sys.version_info < (3, 6),
-                        reason='Fails on Python < 3.6 on Windows, gh-9671')
     @suppress_copy_mask_on_assignment
     def test_varstd_specialcases(self):
         # Test a special case for var
@@ -4603,7 +4605,7 @@ class TestMaskedArrayFunctions:
         class M(MaskedArray):
             pass
 
-        test = np.ma.compressed(M(shape=(0,1,2)))
+        test = np.ma.compressed(M([[[]], [[]]]))
         assert_equal(test.ndim, 1)
 
         # with .compressed() overridden
@@ -4611,7 +4613,7 @@ class TestMaskedArrayFunctions:
             def compressed(self):
                 return 42
 
-        test = np.ma.compressed(M(shape=(0,1,2)))
+        test = np.ma.compressed(M([[[]], [[]]]))
         assert_equal(test, 42)
 
     def test_convolve(self):
diff --git a/numpy/ma/tests/test_old_ma.py b/numpy/ma/tests/test_old_ma.py
index 96c7e3609..ab003b94e 100644
--- a/numpy/ma/tests/test_old_ma.py
+++ b/numpy/ma/tests/test_old_ma.py
@@ -27,7 +27,7 @@ pi = np.pi
 def eq(v, w, msg=''):
     result = allclose(v, w)
     if not result:
-        print("Not eq:%s\n%s\n----%s" % (msg, str(v), str(w)))
+        print(f'Not eq:{msg}\n{v}\n----{w}')
     return result
 
 
diff --git a/numpy/ma/tests/test_subclassing.py b/numpy/ma/tests/test_subclassing.py
index caa746740..f2623406d 100644
--- a/numpy/ma/tests/test_subclassing.py
+++ b/numpy/ma/tests/test_subclassing.py
@@ -109,11 +109,11 @@ class CSAIterator:
 class ComplicatedSubArray(SubArray):
 
     def __str__(self):
-        return 'myprefix {0} mypostfix'.format(self.view(SubArray))
+        return f'myprefix {self.view(SubArray)} mypostfix'
 
     def __repr__(self):
         # Return a repr that does not start with 'name('
-        return '<{0} {1}>'.format(self.__class__.__name__, self)
+        return f'<{self.__class__.__name__} {self}>'
 
     def _validate_input(self, value):
         if not isinstance(value, ComplicatedSubArray):
@@ -317,8 +317,8 @@ class TestSubclassing:
         assert_startswith(repr(mx), 'masked_array')
         xsub = SubArray(x)
         mxsub = masked_array(xsub, mask=[True, False, True, False, False])
-        assert_startswith(repr(mxsub),
-            'masked_{0}(data=[--, 1, --, 3, 4]'.format(SubArray.__name__))
+        assert_startswith(repr(mxsub), 
+            f'masked_{SubArray.__name__}(data=[--, 1, --, 3, 4]')
 
     def test_subclass_str(self):
         """test str with subclass that has overridden str, setitem"""
diff --git a/numpy/ma/testutils.py b/numpy/ma/testutils.py
index 51ab03948..8d55e1763 100644
--- a/numpy/ma/testutils.py
+++ b/numpy/ma/testutils.py
@@ -86,7 +86,7 @@ def _assert_equal_on_sequences(actual, desired, err_msg=''):
     """
     assert_equal(len(actual), len(desired), err_msg)
     for k in range(len(desired)):
-        assert_equal(actual[k], desired[k], 'item=%r\n%s' % (k, err_msg))
+        assert_equal(actual[k], desired[k], f'item={k!r}\n{err_msg}')
     return
 
 
@@ -117,8 +117,8 @@ def assert_equal(actual, desired, err_msg=''):
         assert_equal(len(actual), len(desired), err_msg)
         for k, i in desired.items():
             if k not in actual:
-                raise AssertionError("%s not in %s" % (k, actual))
-            assert_equal(actual[k], desired[k], 'key=%r\n%s' % (k, err_msg))
+                raise AssertionError(f"{k} not in {actual}")
+            assert_equal(actual[k], desired[k], f'key={k!r}\n{err_msg}')
         return
     # Case #2: lists .....
     if isinstance(desired, (list, tuple)) and isinstance(actual, (list, tuple)):
@@ -156,12 +156,12 @@ def fail_if_equal(actual, desired, err_msg='',):
         for k, i in desired.items():
             if k not in actual:
                 raise AssertionError(repr(k))
-            fail_if_equal(actual[k], desired[k], 'key=%r\n%s' % (k, err_msg))
+            fail_if_equal(actual[k], desired[k], f'key={k!r}\n{err_msg}')
         return
     if isinstance(desired, (list, tuple)) and isinstance(actual, (list, tuple)):
         fail_if_equal(len(actual), len(desired), err_msg)
         for k in range(len(desired)):
-            fail_if_equal(actual[k], desired[k], 'item=%r\n%s' % (k, err_msg))
+            fail_if_equal(actual[k], desired[k], f'item={k!r}\n{err_msg}')
         return
     if isinstance(actual, np.ndarray) or isinstance(desired, np.ndarray):
         return fail_if_array_equal(actual, desired, err_msg)
diff --git a/numpy/ma/timer_comparison.py b/numpy/ma/timer_comparison.py
index 83bd7852e..9eb1a23cd 100644
--- a/numpy/ma/timer_comparison.py
+++ b/numpy/ma/timer_comparison.py
@@ -7,12 +7,9 @@ import numpy.core.fromnumeric as fromnumeric
 
 from numpy.testing import build_err_msg
 
-# Fixme: this does not look right.
-np.seterr(all='ignore')
 
 pi = np.pi
 
-
 class ModuleTester:
     def __init__(self, module):
         self.module = module
@@ -77,8 +74,7 @@ class ModuleTester:
             if not cond:
                 msg = build_err_msg([x, y],
                                     err_msg
-                                    + '\n(shapes %s, %s mismatch)' % (x.shape,
-                                                                      y.shape),
+                                    + f'\n(shapes {x.shape}, {y.shape} mismatch)',
                                     header=header,
                                     names=('x', 'y'))
                 assert cond, msg
@@ -100,9 +96,9 @@ class ModuleTester:
                                     header=header,
                                     names=('x', 'y'))
                 assert cond, msg
-        except ValueError:
+        except ValueError as e:
             msg = build_err_msg([x, y], err_msg, header=header, names=('x', 'y'))
-            raise ValueError(msg)
+            raise ValueError(msg) from e
 
     def assert_array_equal(self, x, y, err_msg=''):
         """
@@ -112,6 +108,7 @@ class ModuleTester:
         self.assert_array_compare(self.equal, x, y, err_msg=err_msg,
                                   header='Arrays are not equal')
 
+    @np.errstate(all='ignore')
     def test_0(self):
         """
         Tests creation
@@ -122,6 +119,7 @@ class ModuleTester:
         xm = self.masked_array(x, mask=m)
         xm[0]
 
+    @np.errstate(all='ignore')
     def test_1(self):
         """
         Tests creation
@@ -149,6 +147,7 @@ class ModuleTester:
             xf.shape = s
             assert(self.count(xm) == len(m1) - reduce(lambda x, y:x+y, m1))
 
+    @np.errstate(all='ignore')
     def test_2(self):
         """
         Tests conversions and indexing.
@@ -191,6 +190,7 @@ class ModuleTester:
         m3 = self.make_mask(m, copy=1)
         assert(m is not m3)
 
+    @np.errstate(all='ignore')
     def test_3(self):
         """
         Tests resize/repeat
@@ -210,6 +210,7 @@ class ModuleTester:
         y8 = x4.repeat(2, 0)
         assert self.allequal(y5, y8)
 
+    @np.errstate(all='ignore')
     def test_4(self):
         """
         Test of take, transpose, inner, outer products.
@@ -233,6 +234,7 @@ class ModuleTester:
         assert t[1] == 2
         assert t[2] == 3
 
+    @np.errstate(all='ignore')
     def test_5(self):
         """
         Tests inplace w/ scalar
@@ -285,6 +287,7 @@ class ModuleTester:
         x += 1.
         assert self.allequal(x, y + 1.)
 
+    @np.errstate(all='ignore')
     def test_6(self):
         """
         Tests inplace w/ array
@@ -336,6 +339,7 @@ class ModuleTester:
         x /= a
         xm /= a
 
+    @np.errstate(all='ignore')
     def test_7(self):
         "Tests ufunc"
         d = (self.array([1.0, 0, -1, pi/2]*2, mask=[0, 1]+[0]*6),
@@ -370,6 +374,7 @@ class ModuleTester:
             self.assert_array_equal(ur.filled(0), mr.filled(0), f)
             self.assert_array_equal(ur._mask, mr._mask)
 
+    @np.errstate(all='ignore')
     def test_99(self):
         # test average
         ott = self.array([0., 1., 2., 3.], mask=[1, 0, 0, 0])
@@ -415,6 +420,7 @@ class ModuleTester:
         self.assert_array_equal(self.average(z, axis=1), [2.5, 5.0])
         self.assert_array_equal(self.average(z, axis=0, weights=w2), [0., 1., 99., 99., 4.0, 10.0])
 
+    @np.errstate(all='ignore')
     def test_A(self):
         x = self.arange(24)
         x[5:6] = self.masked
@@ -434,4 +440,4 @@ if __name__ == '__main__':
         cur = np.sort(cur)
         print("#%i" % i + 50*'.')
         print(eval("ModuleTester.test_%i.__doc__" % i))
-        print("core_current : %.3f - %.3f" % (cur[0], cur[1]))
+        print(f'core_current : {cur[0]:.3f} - {cur[1]:.3f}')