MAINT Use list and dict comprehension (pandas-dev#23894)

pandas/core/computation/align.py

@@ -30,9 +30,8 @@ def _align_core_single_unary_op(term):
 
 
 def _zip_axes_from_type(typ, new_axes):
-    axes = {}
-    for ax_ind, ax_name in compat.iteritems(typ._AXIS_NAMES):
-        axes[ax_name] = new_axes[ax_ind]
+    axes = {ax_name: new_axes[ax_ind]
+            for ax_ind, ax_name in compat.iteritems(typ._AXIS_NAMES)}
     return axes
 
 

pandas/core/config.py

@@ -395,11 +395,8 @@ def __init__(self, *args):
         self.ops = list(zip(args[::2], args[1::2]))
 
     def __enter__(self):
-        undo = []
-        for pat, val in self.ops:
-            undo.append((pat, _get_option(pat, silent=True)))
-
-        self.undo = undo
+        self.undo = [(pat, _get_option(pat, silent=True))
+                     for pat, val in self.ops]
 
         for pat, val in self.ops:
             _set_option(pat, val, silent=True)

pandas/core/dtypes/concat.py

@@ -373,10 +373,8 @@ def _maybe_unwrap(x):
         if sort_categories:
             categories = categories.sort_values()
 
-        new_codes = []
-        for c in to_union:
-            new_codes.append(_recode_for_categories(c.codes, c.categories,
-                                                    categories))
+        new_codes = [_recode_for_categories(c.codes, c.categories, categories)
+                     for c in to_union]
         new_codes = np.concatenate(new_codes)
     else:
         # ordered - to show a proper error message

pandas/core/frame.py

@@ -3569,11 +3569,8 @@ def reindexer(value):
 
     @property
     def _series(self):
-        result = {}
-        for idx, item in enumerate(self.columns):
-            result[item] = Series(self._data.iget(idx), index=self.index,
-                                  name=item)
-        return result
+        return {item: Series(self._data.iget(idx), index=self.index, name=item)
+                for idx, item in enumerate(self.columns)}
 
     def lookup(self, row_labels, col_labels):
         """
@@ -3593,9 +3590,8 @@ def lookup(self, row_labels, col_labels):
         -----
         Akin to::
 
-            result = []
-            for row, col in zip(row_labels, col_labels):
-                result.append(df.get_value(row, col))
+            result = [df.get_value(row, col)
+                      for row, col in zip(row_labels, col_labels)]
 
         Examples
         --------
@@ -4600,10 +4596,8 @@ def sort_values(self, by, axis=0, ascending=True, inplace=False,
         if len(by) > 1:
             from pandas.core.sorting import lexsort_indexer
 
-            keys = []
-            for x in by:
-                k = self._get_label_or_level_values(x, axis=axis)
-                keys.append(k)
+            keys = [self._get_label_or_level_values(x, axis=axis)
+                    for x in by]
             indexer = lexsort_indexer(keys, orders=ascending,
                                       na_position=na_position)
             indexer = ensure_platform_int(indexer)

pandas/core/groupby/ops.py

@@ -678,10 +678,8 @@ def groups(self):
 
         # this is mainly for compat
         # GH 3881
-        result = {}
-        for key, value in zip(self.binlabels, self.bins):
-            if key is not NaT:
-                result[key] = value
+        result = {key: value for key, value in zip(self.binlabels, self.bins)
+                  if key is not NaT}
         return result
 
     @property

pandas/core/internals/blocks.py

@@ -2295,10 +2295,7 @@ def convert(self, *args, **kwargs):
                          'convert_timedeltas']
         fn_inputs += ['copy']
 
-        fn_kwargs = {}
-        for key in fn_inputs:
-            if key in kwargs:
-                fn_kwargs[key] = kwargs[key]
+        fn_kwargs = {key: kwargs[key] for key in fn_inputs if key in kwargs}
 
         # operate column-by-column
         def f(m, v, i):

pandas/core/panel.py

@@ -336,9 +336,8 @@ def _compare_constructor(self, other, func):
             raise Exception('Can only compare identically-labeled '
                             'same type objects')
 
-        new_data = {}
-        for col in self._info_axis:
-            new_data[col] = func(self[col], other[col])
+        new_data = {col: func(self[col], other[col])
+                    for col in self._info_axis}
 
         d = self._construct_axes_dict(copy=False)
         return self._constructor(data=new_data, **d)
@@ -949,9 +948,8 @@ def to_frame(self, filter_observations=True):
             # size = N * K
             selector = slice(None, None)
 
-        data = {}
-        for item in self.items:
-            data[item] = self[item].values.ravel()[selector]
+        data = {item: self[item].values.ravel()[selector]
+                for item in self.items}
 
         def construct_multi_parts(idx, n_repeat, n_shuffle=1):
             # Replicates and shuffles MultiIndex, returns individual attributes

pandas/core/reshape/melt.py

@@ -448,9 +448,8 @@ def melt_stub(df, stub, i, j, value_vars, sep):
     value_vars_flattened = [e for sublist in value_vars for e in sublist]
     id_vars = list(set(df.columns.tolist()).difference(value_vars_flattened))
 
-    melted = []
-    for s, v in zip(stubnames, value_vars):
-        melted.append(melt_stub(df, s, i, j, v, sep))
+    melted = [melt_stub(df, s, i, j, v, sep)
+              for s, v in zip(stubnames, value_vars)]
     melted = melted[0].join(melted[1:], how='outer')
 
     if len(i) == 1:

pandas/core/sparse/frame.py

@@ -339,9 +339,8 @@ def to_dense(self):
     def _apply_columns(self, func):
         """ get new SparseDataFrame applying func to each columns """
 
-        new_data = {}
-        for col, series in compat.iteritems(self):
-            new_data[col] = func(series)
+        new_data = {col: func(series)
+                    for col, series in compat.iteritems(self)}
 
         return self._constructor(
             data=new_data, index=self.index, columns=self.columns,

pandas/core/window.py

@@ -2479,9 +2479,8 @@ def dataframe_from_int_dict(data, frame_template):
             else:
                 raise ValueError("'pairwise' is not True/False")
         else:
-            results = {}
-            for i, col in enumerate(arg1.columns):
-                results[i] = f(*_prep_binary(arg1.iloc[:, i], arg2))
+            results = {i: f(*_prep_binary(arg1.iloc[:, i], arg2))
+                       for i, col in enumerate(arg1.columns)}
             return dataframe_from_int_dict(results, arg1)
 
     else:

pandas/io/excel.py

@@ -586,10 +586,9 @@ def _parse_cell(cell_contents, cell_typ):
             usecols = _maybe_convert_usecols(usecols)
 
             for i in range(sheet.nrows):
-                row = []
-                for j, (value, typ) in enumerate(zip(sheet.row_values(i),
-                                                     sheet.row_types(i))):
-                    row.append(_parse_cell(value, typ))
+                row = [_parse_cell(value, typ)
+                       for value, typ in zip(sheet.row_values(i),
+                                             sheet.row_types(i))]
                 data.append(row)
 
             if sheet.nrows == 0:

pandas/io/formats/printing.py

@@ -110,10 +110,10 @@ def _pprint_seq(seq, _nest_lvl=0, max_seq_items=None, **kwds):
         nitems = max_seq_items or get_option("max_seq_items") or len(seq)
 
     s = iter(seq)
-    r = []
-    for i in range(min(nitems, len(seq))):  # handle sets, no slicing
-        r.append(pprint_thing(
-            next(s), _nest_lvl + 1, max_seq_items=max_seq_items, **kwds))
+    # handle sets, no slicing
+    r = [pprint_thing(next(s),
+                      _nest_lvl + 1, max_seq_items=max_seq_items, **kwds)
+         for i in range(min(nitems, len(seq)))]
     body = ", ".join(r)
 
     if nitems < len(seq):

pandas/io/formats/style.py

@@ -1349,10 +1349,8 @@ def _get_level_lengths(index, hidden_elements=None):
             elif(j not in hidden_elements):
                 lengths[(i, last_label)] += 1
 
-    non_zero_lengths = {}
-    for element, length in lengths.items():
-        if(length >= 1):
-            non_zero_lengths[element] = length
+    non_zero_lengths = {
+        element: length for element, length in lengths.items() if length >= 1}
 
     return non_zero_lengths
 

pandas/io/sas/sas_xport.py

@@ -353,9 +353,8 @@ def _read_header(self):
         self.columns = [x['name'].decode() for x in self.fields]
 
         # Setup the dtype.
-        dtypel = []
-        for i, field in enumerate(self.fields):
-            dtypel.append(('s' + str(i), "S" + str(field['field_length'])))
+        dtypel = [('s' + str(i), "S" + str(field['field_length']))
+                  for i, field in enumerate(self.fields)]
         dtype = np.dtype(dtypel)
         self._dtype = dtype
 

pandas/io/stata.py

@@ -2947,10 +2947,10 @@ def _update_strl_names(self):
     def _convert_strls(self, data):
         """Convert columns to StrLs if either very large or in the
         convert_strl variable"""
-        convert_cols = []
-        for i, col in enumerate(data):
-            if self.typlist[i] == 32768 or col in self._convert_strl:
-                convert_cols.append(col)
+        convert_cols = [
+            col for i, col in enumerate(data)
+            if self.typlist[i] == 32768 or col in self._convert_strl]
+
         if convert_cols:
             ssw = StataStrLWriter(data, convert_cols)
             tab, new_data = ssw.generate_table()

pandas/plotting/_core.py

@@ -157,9 +157,8 @@ def __init__(self, data, kind=None, by=None, subplots=False, sharex=None,
         # parse errorbar input if given
         xerr = kwds.pop('xerr', None)
         yerr = kwds.pop('yerr', None)
-        self.errors = {}
-        for kw, err in zip(['xerr', 'yerr'], [xerr, yerr]):
-            self.errors[kw] = self._parse_errorbars(kw, err)
+        self.errors = {kw: self._parse_errorbars(kw, err)
+                       for kw, err in zip(['xerr', 'yerr'], [xerr, yerr])}
 
         if not isinstance(secondary_y, (bool, tuple, list,
                                         np.ndarray, ABCIndexClass)):
@@ -1721,9 +1720,7 @@ def result(self):
 _klasses = [LinePlot, BarPlot, BarhPlot, KdePlot, HistPlot, BoxPlot,
             ScatterPlot, HexBinPlot, AreaPlot, PiePlot]
 
-_plot_klass = {}
-for klass in _klasses:
-    _plot_klass[klass._kind] = klass
+_plot_klass = {klass._kind: klass for klass in _klasses}
 
 
 def _plot(data, x=None, y=None, subplots=False,

pandas/tests/frame/test_axis_select_reindex.py

@@ -634,9 +634,7 @@ def test_align(self):
 
         left, right = self.frame.align(s, broadcast_axis=1)
         tm.assert_index_equal(left.index, self.frame.index)
-        expected = {}
-        for c in self.frame.columns:
-            expected[c] = s
+        expected = {c: s for c in self.frame.columns}
         expected = DataFrame(expected, index=self.frame.index,
                              columns=self.frame.columns)
         tm.assert_frame_equal(right, expected)

pandas/tests/frame/test_indexing.py

@@ -1782,11 +1782,9 @@ def test_get_value(self):
 
     def test_lookup(self):
         def alt(df, rows, cols, dtype):
-            result = []
-            for r, c in zip(rows, cols):
-                with tm.assert_produces_warning(FutureWarning,
-                                                check_stacklevel=False):
-                    result.append(df.get_value(r, c))
+            with tm.assert_produces_warning(FutureWarning,
+                                            check_stacklevel=False):
+                result = [df.get_value(r, c) for r, c in zip(rows, cols)]
             return np.array(result, dtype=dtype)
 
         def testit(df):

pandas/tests/frame/test_replace.py

@@ -806,9 +806,8 @@ def test_replace_input_formats_listlike(self):
         df = DataFrame({'A': [np.nan, 0, np.inf], 'B': [0, 2, 5],
                         'C': ['', 'asdf', 'fd']})
         filled = df.replace(to_rep, values)
-        expected = {}
-        for k, v in compat.iteritems(df):
-            expected[k] = v.replace(to_rep[k], values[k])
+        expected = {k: v.replace(to_rep[k], values[k])
+                    for k, v in compat.iteritems(df)}
         assert_frame_equal(filled, DataFrame(expected))
 
         result = df.replace([0, 2, 5], [5, 2, 0])
@@ -821,9 +820,8 @@ def test_replace_input_formats_listlike(self):
         df = DataFrame({'A': [np.nan, 0, np.nan], 'B': [0, 2, 5],
                         'C': ['', 'asdf', 'fd']})
         filled = df.replace(np.nan, values)
-        expected = {}
-        for k, v in compat.iteritems(df):
-            expected[k] = v.replace(np.nan, values[k])
+        expected = {k: v.replace(np.nan, values[k])
+                    for k, v in compat.iteritems(df)}
         assert_frame_equal(filled, DataFrame(expected))
 
         # list to list
@@ -844,9 +842,8 @@ def test_replace_input_formats_scalar(self):
         # dict to scalar
         to_rep = {'A': np.nan, 'B': 0, 'C': ''}
         filled = df.replace(to_rep, 0)
-        expected = {}
-        for k, v in compat.iteritems(df):
-            expected[k] = v.replace(to_rep[k], 0)
+        expected = {k: v.replace(to_rep[k], 0)
+                    for k, v in compat.iteritems(df)}
         assert_frame_equal(filled, DataFrame(expected))
 
         pytest.raises(TypeError, df.replace, to_rep, [np.nan, 0, ''])

pandas/tests/generic/test_generic.py

@@ -92,9 +92,8 @@ def test_rename(self):
     def test_get_numeric_data(self):
 
         n = 4
-        kwargs = {}
-        for i in range(self._ndim):
-            kwargs[self._typ._AXIS_NAMES[i]] = list(range(n))
+        kwargs = {self._typ._AXIS_NAMES[i]: list(range(n))
+                  for i in range(self._ndim)}
 
         # get the numeric data
         o = self._construct(n, **kwargs)

pandas/tests/groupby/aggregate/test_cython.py

@@ -45,9 +45,7 @@ def test_cythonized_aggers(op_name):
 
     # single column
     grouped = df.drop(['B'], axis=1).groupby('A')
-    exp = {}
-    for cat, group in grouped:
-        exp[cat] = op(group['C'])
+    exp = {cat: op(group['C']) for cat, group in grouped}
     exp = DataFrame({'C': exp})
     exp.index.name = 'A'
     result = op(grouped)

pandas/tests/groupby/test_groupby.py

@@ -348,9 +348,7 @@ def test_attr_wrapper(ts):
 
     # this is pretty cool
     result = grouped.describe()
-    expected = {}
-    for name, gp in grouped:
-        expected[name] = gp.describe()
+    expected = {name: gp.describe() for name, gp in grouped}
     expected = DataFrame(expected).T
     assert_frame_equal(result, expected)
 
@@ -1312,19 +1310,15 @@ def test_skip_group_keys():
     grouped = tsf.groupby(lambda x: x.month, group_keys=False)
     result = grouped.apply(lambda x: x.sort_values(by='A')[:3])
 
-    pieces = []
-    for key, group in grouped:
-        pieces.append(group.sort_values(by='A')[:3])
+    pieces = [group.sort_values(by='A')[:3] for key, group in grouped]
 
     expected = pd.concat(pieces)
     assert_frame_equal(result, expected)
 
     grouped = tsf['A'].groupby(lambda x: x.month, group_keys=False)
     result = grouped.apply(lambda x: x.sort_values()[:3])
 
-    pieces = []
-    for key, group in grouped:
-        pieces.append(group.sort_values()[:3])
+    pieces = [group.sort_values()[:3] for key, group in grouped]
 
     expected = pd.concat(pieces)
     assert_series_equal(result, expected)

pandas/tests/groupby/test_grouping.py

@@ -727,9 +727,7 @@ def test_multi_iter_frame(self, three_group):
         df['k1'] = np.array(['b', 'b', 'b', 'a', 'a', 'a'])
         df['k2'] = np.array(['1', '1', '1', '2', '2', '2'])
         grouped = df.groupby(['k1', 'k2'])
-        groups = {}
-        for key, gp in grouped:
-            groups[key] = gp
+        groups = {key: gp for key, gp in grouped}
         assert len(groups) == 2
 
         # axis = 1