BUG: unclosed file warning when passing invalid encoding (pandas-dev#30034)

Author: jbrockmendel

pandas/io/formats/format.py

@@ -3,7 +3,6 @@
 and latex files. This module also applies to display formatting.
 """
 
-import codecs
 from contextlib import contextmanager
 from datetime import tzinfo
 import decimal
@@ -495,7 +494,11 @@ def get_buffer(
         if hasattr(buf, "write"):
             yield buf
         elif isinstance(buf, str):
-            with codecs.open(buf, "w", encoding=encoding) as f:
+            with open(buf, "w", encoding=encoding, newline="") as f:
+                # GH#30034 open instead of codecs.open prevents a file leak
+                #  if we have an invalid encoding argument.
+                # newline="" is needed to roundtrip correctly on
+                #  windows test_to_latex_filename
                 yield f
         else:
             raise TypeError("buf is not a file name and it has no write method")

pandas/tests/io/formats/test_format.py

@@ -3259,8 +3259,9 @@ def test_filepath_or_buffer_arg(
         ):
             getattr(df, method)(buf=filepath_or_buffer, encoding=encoding)
     elif encoding == "foo":
-        with pytest.raises(LookupError, match="unknown encoding"):
-            getattr(df, method)(buf=filepath_or_buffer, encoding=encoding)
+        with tm.assert_produces_warning(None):
+            with pytest.raises(LookupError, match="unknown encoding"):
+                getattr(df, method)(buf=filepath_or_buffer, encoding=encoding)
     else:
         expected = getattr(df, method)()
         getattr(df, method)(buf=filepath_or_buffer, encoding=encoding)