Enable pylint undefined-loop-variable warning (#50961)

* Enable pylint undefined-loop-variable check

* Respond to review comments

Author: uzzell

pandas/core/util/hashing.py

@@ -71,12 +71,14 @@ def combine_hash_arrays(
 
     mult = np.uint64(1000003)
     out = np.zeros_like(first) + np.uint64(0x345678)
+    last_i = 0
     for i, a in enumerate(arrays):
         inverse_i = num_items - i
         out ^= a
         out *= mult
         mult += np.uint64(82520 + inverse_i + inverse_i)
-    assert i + 1 == num_items, "Fed in wrong num_items"
+        last_i = i
+    assert last_i + 1 == num_items, "Fed in wrong num_items"
     out += np.uint64(97531)
     return out
 

pandas/io/excel/_base.py

@@ -736,7 +736,9 @@ def parse(
 
         output = {}
 
+        last_sheetname = None
         for asheetname in sheets:
+            last_sheetname = asheetname
             if verbose:
                 print(f"Reading sheet {asheetname}")
 
@@ -888,10 +890,13 @@ def parse(
                 err.args = (f"{err.args[0]} (sheet: {asheetname})", *err.args[1:])
                 raise err
 
+        if last_sheetname is None:
+            raise ValueError("Sheet name is an empty list")
+
         if ret_dict:
             return output
         else:
-            return output[asheetname]
+            return output[last_sheetname]
 
 
 @doc(storage_options=_shared_docs["storage_options"])

pandas/tests/frame/methods/test_to_dict_of_blocks.py

@@ -20,30 +20,34 @@ def test_copy_blocks(self, float_frame):
         column = df.columns[0]
 
         # use the default copy=True, change a column
+        _last_df = None
         blocks = df._to_dict_of_blocks(copy=True)
         for _df in blocks.values():
+            _last_df = _df
             if column in _df:
                 _df.loc[:, column] = _df[column] + 1
 
         # make sure we did not change the original DataFrame
-        assert not _df[column].equals(df[column])
+        assert _last_df is not None and not _last_df[column].equals(df[column])
 
     def test_no_copy_blocks(self, float_frame, using_copy_on_write):
         # GH#9607
         df = DataFrame(float_frame, copy=True)
         column = df.columns[0]
 
+        _last_df = None
         # use the copy=False, change a column
         blocks = df._to_dict_of_blocks(copy=False)
         for _df in blocks.values():
+            _last_df = _df
             if column in _df:
                 _df.loc[:, column] = _df[column] + 1
 
         if not using_copy_on_write:
             # make sure we did change the original DataFrame
-            assert _df[column].equals(df[column])
+            assert _last_df is not None and _last_df[column].equals(df[column])
         else:
-            assert not _df[column].equals(df[column])
+            assert _last_df is not None and not _last_df[column].equals(df[column])
 
 
 def test_to_dict_of_blocks_item_cache(request, using_copy_on_write):

pandas/tests/io/formats/test_printing.py

@@ -122,22 +122,24 @@ class TestTableSchemaRepr:
     def test_publishes(self, ip):
         ipython = ip.instance(config=ip.config)
         df = pd.DataFrame({"A": [1, 2]})
-        objects = [df["A"], df, df]  # dataframe / series
+        objects = [df["A"], df]  # dataframe / series
         expected_keys = [
             {"text/plain", "application/vnd.dataresource+json"},
             {"text/plain", "text/html", "application/vnd.dataresource+json"},
         ]
 
         opt = pd.option_context("display.html.table_schema", True)
+        last_obj = None
         for obj, expected in zip(objects, expected_keys):
+            last_obj = obj
             with opt:
                 formatted = ipython.display_formatter.format(obj)
             assert set(formatted[0].keys()) == expected
 
         with_latex = pd.option_context("styler.render.repr", "latex")
 
         with opt, with_latex:
-            formatted = ipython.display_formatter.format(obj)
+            formatted = ipython.display_formatter.format(last_obj)
 
         expected = {
             "text/plain",

pyproject.toml

@@ -287,7 +287,6 @@ disable = [
   "too-many-public-methods",
   "too-many-return-statements",
   "too-many-statements",
-  "undefined-loop-variable",
   "unexpected-keyword-arg",
   "ungrouped-imports",
   "unsubscriptable-object",