Description

picnixz

opened on Aug 9, 2026

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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.

cc @gpshead @hugovk

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-155419: honor the file object's current position in hashlib.file_digest #155422

Activity

1. picnixz

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Aug 9, 2026
2. picnixz

   added a parent issue on Aug 9, 2026

   • Meta-issue for bugs in Lib/hmac.py and Lib/hashlib.py #155413
3. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Aug 9, 2026
4. picnixz

   self-assigned this

   on Aug 9, 2026
5. picnixz commented on Aug 9, 2026

   

   picnixz

   on Aug 9, 2026

   MemberAuthor

   More actions

   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.

   Reacted by Cody Maloney
6. picnixz

   added 3 commits that reference this issue on Aug 9, 2026

   pythongh-155419: honor the file object's current position in `hashlib

   d81a4ff

   pythongh-155419: honor the file object's current position in `hashlib

   ac01ec2

   pythongh-155419: honor the file object's current position in `hashlib

   6817e92
7. picnixz

   added 3 commits that reference this issue on Oct 23, 2026

   pythongh-155419: use the `hashlib.file_digest` fast path for `io.Byte…

   8b5acae

   pythongh-155419: test that importing `hashlib` does not import `io`

   644ac60

   pythongh-155419: test `hashlib.file_digest` on a non-`io.BytesIO` buffer

   7309e0f

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