STY: use pytest.raises context syntax (indexing)

pandas/tests/indexing/multiindex/test_loc.py

@@ -123,10 +123,12 @@ def test_loc_multiindex(self):
         tm.assert_frame_equal(rs, xp)
 
         # missing label
-        pytest.raises(KeyError, lambda: mi_int.loc[2])
+        with pytest.raises(KeyError, match=r"^2L?$"):
+            mi_int.loc[2]
         with catch_warnings(record=True):
             # GH 21593
-            pytest.raises(KeyError, lambda: mi_int.ix[2])
+            with pytest.raises(KeyError, match=r"^2L?$"):
+                mi_int.ix[2]
 
     def test_loc_multiindex_indexer_none(self):
 

pandas/tests/indexing/multiindex/test_partial.py

@@ -104,8 +104,8 @@ def test_getitem_partial_column_select(self):
             result = df.ix[('a', 'y'), [1, 0]]
         tm.assert_frame_equal(result, expected)
 
-        pytest.raises(KeyError, df.loc.__getitem__,
-                      (('a', 'foo'), slice(None, None)))
+        with pytest.raises(KeyError, match=r"\('a', 'foo'\)"):
+            df.loc[('a', 'foo'), :]
 
     def test_partial_set(
             self, multiindex_year_month_day_dataframe_random_data):

pandas/tests/indexing/multiindex/test_slice.py

@@ -107,7 +107,8 @@ def test_per_axis_per_level_getitem(self):
         # ambiguous cases
         # these can be multiply interpreted (e.g. in this case
         # as df.loc[slice(None),[1]] as well
-        pytest.raises(KeyError, lambda: df.loc[slice(None), [1]])
+        with pytest.raises(KeyError, match=r"'\[1\] not in index'"):
+            df.loc[slice(None), [1]]
 
         result = df.loc[(slice(None), [1]), :]
         expected = df.iloc[[0, 3]]

pandas/tests/indexing/test_categorical.py

@@ -53,23 +53,20 @@ def test_loc_scalar(self):
         assert_frame_equal(df, expected)
 
         # value not in the categories
-        pytest.raises(KeyError, lambda: df.loc['d'])
+        with pytest.raises(KeyError, match=r"^'d'$"):
+            df.loc['d']
 
-        def f():
+        msg = "cannot append a non-category item to a CategoricalIndex"
+        with pytest.raises(TypeError, match=msg):
             df.loc['d'] = 10
 
-        pytest.raises(TypeError, f)
-
-        def f():
+        msg = ("cannot insert an item into a CategoricalIndex that is not"
+               " already an existing category")
+        with pytest.raises(TypeError, match=msg):
             df.loc['d', 'A'] = 10
-
-        pytest.raises(TypeError, f)
-
-        def f():
+        with pytest.raises(TypeError, match=msg):
             df.loc['d', 'C'] = 10
 
-        pytest.raises(TypeError, f)
-
     def test_getitem_scalar(self):
 
         cats = Categorical([Timestamp('12-31-1999'),
@@ -318,7 +315,8 @@ def test_loc_listlike(self):
         assert_frame_equal(result, expected, check_index_type=True)
 
         # element in the categories but not in the values
-        pytest.raises(KeyError, lambda: self.df2.loc['e'])
+        with pytest.raises(KeyError, match=r"^'e'$"):
+            self.df2.loc['e']
 
         # assign is ok
         df = self.df2.copy()
@@ -616,22 +614,29 @@ def test_reindexing(self):
         assert_frame_equal(result, expected, check_index_type=True)
 
         # passed duplicate indexers are not allowed
-        pytest.raises(ValueError, lambda: self.df2.reindex(['a', 'a']))
+        msg = "cannot reindex with a non-unique indexer"
+        with pytest.raises(ValueError, match=msg):
+            self.df2.reindex(['a', 'a'])
 
         # args NotImplemented ATM
-        pytest.raises(NotImplementedError,
-                      lambda: self.df2.reindex(['a'], method='ffill'))
-        pytest.raises(NotImplementedError,
-                      lambda: self.df2.reindex(['a'], level=1))
-        pytest.raises(NotImplementedError,
-                      lambda: self.df2.reindex(['a'], limit=2))
+        msg = r"argument {} is not implemented for CategoricalIndex\.reindex"
+        with pytest.raises(NotImplementedError, match=msg.format('method')):
+            self.df2.reindex(['a'], method='ffill')
+        with pytest.raises(NotImplementedError, match=msg.format('level')):
+            self.df2.reindex(['a'], level=1)
+        with pytest.raises(NotImplementedError, match=msg.format('limit')):
+            self.df2.reindex(['a'], limit=2)
 
     def test_loc_slice(self):
         # slicing
         # not implemented ATM
         # GH9748
 
-        pytest.raises(TypeError, lambda: self.df.loc[1:5])
+        msg = ("cannot do slice indexing on {klass} with these "
+               r"indexers \[1\] of {kind}".format(
+                   klass=str(CategoricalIndex), kind=str(int)))
+        with pytest.raises(TypeError, match=msg):
+            self.df.loc[1:5]
 
         # result = df.loc[1:5]
         # expected = df.iloc[[1,2,3,4]]
@@ -679,8 +684,11 @@ def test_boolean_selection(self):
         #         categories=[3, 2, 1],
         #         ordered=False,
         #         name=u'B')
-        pytest.raises(TypeError, lambda: df4[df4.index < 2])
-        pytest.raises(TypeError, lambda: df4[df4.index > 1])
+        msg = "Unordered Categoricals can only compare equality or not"
+        with pytest.raises(TypeError, match=msg):
+            df4[df4.index < 2]
+        with pytest.raises(TypeError, match=msg):
+            df4[df4.index > 1]
 
     def test_indexing_with_category(self):
 

pandas/tests/indexing/test_chaining_and_caching.py

@@ -302,11 +302,11 @@ def test_setting_with_copy_bug(self):
                         'c': ['a', 'b', np.nan, 'd']})
         mask = pd.isna(df.c)
 
-        def f():
+        msg = ("A value is trying to be set on a copy of a slice from a"
+               " DataFrame")
+        with pytest.raises(com.SettingWithCopyError, match=msg):
             df[['c']][mask] = df[['b']][mask]
 
-        pytest.raises(com.SettingWithCopyError, f)
-
         # invalid warning as we are returning a new object
         # GH 8730
         df1 = DataFrame({'x': Series(['a', 'b', 'c']),