QUERY · ISSUE

FileIO is not a subclass of IOBase

openby tveopened 2020-01-24updated 2021-09-26

py-core

E.g.:

>>> f = open("boot.py", 'rb')
>>> f
<io.FileIO 3ffe6480>
>>> import io
>>> isinstance(f, io.IOBase)
False

Needless to say, the result in CPython is True.

CANDIDATE · ISSUE

py/modio.c Can this be made to work in Unix build?

closedby peterhinchopened 2018-11-10updated 2018-11-15

The ability to subclass io.IOBase is unavailable under Unix. It would be good if this were remedied.

Assessment

S Sonnet · high

Both issues involve io.IOBase in MicroPython's py/modio.c, but they describe distinct problems. #5570 is a bug: built-in FileIO objects fail isinstance(f, io.IOBase) — the existing class hierarchy is broken. #4299 is a feature request: user-defined classes cannot subclass io.IOBase in the Unix build at all. Fixing one does not necessarily fix the other: restoring the FileIO→IOBase inheritance chain doesn't enable user subclassing in Unix, and enabling user subclassing doesn't fix how isinstance resolves the existing FileIO type. They share the same module and concept space but require separate fixes.

Suggested action

Link the two issues as related context when working on io.IOBase improvements. Fixing the class hierarchy for #5570 may expose or inform the Unix subclassing gap in #4299, so cross-reference them but keep them open independently.

FileIO is not a subclass of IOBase

py/modio.c Can this be made to work in Unix build?

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