Fix types

Author: jonashaag

pandas/io/common.py

@@ -63,7 +63,7 @@
 # to get it through `zstd.open`.
 try:
     with import_optional_dependency("zstandard").open(io.BytesIO()) as reader:
-        _ZstdDecompressorReader = type(reader)
+        _ZstdDecompressorReader: type | None = type(reader)
 except ImportError:
     _ZstdDecompressorReader = None
 
@@ -1050,8 +1050,10 @@ def _is_binary_mode(handle: FilePathOrBuffer, mode: str) -> bool:
         return False
 
     # classes that expect bytes
-    binary_classes = (BufferedIOBase, RawIOBase)
+    binary_classes = [BufferedIOBase, RawIOBase]
     # Zstandard doesn't use any of the builtin base classes
     if _ZstdDecompressorReader is not None:
-        binary_classes += (_ZstdDecompressorReader,)
-    return isinstance(handle, binary_classes) or "b" in getattr(handle, "mode", mode)
+        binary_classes.append(_ZstdDecompressorReader)
+    is_binary_class = isinstance(handle, tuple(binary_classes))
+
+    return is_binary_class or "b" in getattr(handle, "mode", mode)

pandas/tests/io/test_common.py

@@ -12,6 +12,10 @@
 import os
 from pathlib import Path
 import tempfile
+from typing import (
+    Optional,
+    cast,
+)
 
 import pytest
 
@@ -101,7 +105,7 @@ def test_stringify_file_and_path_like(self):
 
     @pytest.mark.parametrize(
         "extension,expected",
-        [("", None)]
+        [("", cast(Optional[str], None))]
         + [
             (f".{ext}", compression)
             for compression, ext in icom._compression_to_extension.items()