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hashlib.file_digest does not honor current position for io.BytesIO inputs #155419
Description
Bug report
Bug description:
hashlib.file_digest() takes a getbuffer() fast path that hashes the entire buffer regardless of tell(), so the same bytes at the same position give a different digest for io.BytesIO than for a real binary file.
We never had tests to exercise that behavior and we never got report about it. I want to sync the merges of all PRs at once so that the behavior is fixed simultaneously before the next release.
CPython versions tested on:
CPython main branch
Operating systems tested on:
No response
Activity
Lib/hmac.pyandLib/hashlib.py#155413picnixz commentedon Aug 9, 2026
I decided to fix this instead of document the inconsistency because when not given a io.BytesIO object, we are actually honoring the position. So it's a bug.
pythongh-155419: honor the file object's current position in `hashlib
pythongh-155419: honor the file object's current position in `hashlib
pythongh-155419: honor the file object's current position in `hashlib