ENH: Remove `mode` property from `BaseBuffer`

[ethantkoenig]

Feature Type

• Adding new functionality to pandas

• Changing existing functionality in pandas

• Removing existing functionality in pandas

Problem Description

I would like to pass an io.IOBase (or a subclass, such as botocore.response.StreamingBody) to functions that accept one of the various "buffer" classes (ReadBuffer, ReadCsvBuffer, etc.)

Currently, this does not type-check (or, at least not with Pyright), because the BaseBuffer protocol defines a mode property:

pandas/pandas/_typing.py

Lines 271 to 274 in 1be2637

	@property
	def mode(self) -> str:
	# for _get_filepath_or_buffer
	...

Type "IOBase" is not assignable to declared type "ReadCsvBuffer[bytes]"
  "IOBase" is incompatible with protocol "ReadCsvBuffer[bytes]"
    "mode" is not present

Feature Description

AFAICT, the only place the BaseBuffer.mode property is accessed is this getattr call, which can handle the property not existing (due to the default value).

pandas/pandas/io/common.py

Lines 1196 to 1198 in 1be2637

	return isinstance(handle, _get_binary_io_classes()) or "b" in getattr(
	handle, "mode", mode
	)

Can we just remove the mode property from BaseBuffer, since (AFAICT) it's not actually required by any Pandas code that handles BaseBuffer instances (and/or instances of BaseBuffer subclasses)?

Alternative Solutions

If python/typing#601 ever becomes a reality, BaseBuffer.mode could be marked as an "optional" property.

Additional Context

No response