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gh-73199: Fix incorrect zip64 threshold in doc #152472

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gh-73199: Fix incorrect zip64 threshold in doc #152472

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gh-73199: Fix incorrect zip64 threshold in doc
danny0838 Jun 28, 2026
93d54a9
Minor rephrase
danny0838 Jul 4, 2026
aed82dc
Rephrase another inaccurate statement
danny0838 Jul 4, 2026
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12 changes: 7 additions & 5 deletions Doc/library/zipfile.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ defined in `PKZIP Application Note`_.

This module does not handle multipart ZIP files.
It can handle ZIP files that use the ZIP64 extensions
(that is ZIP files that are more than 4 GiB in size). It supports
(mostly for ZIP files larger than 4 GiB). It supports

@StanFromIreland StanFromIreland Oct 23, 2026

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This should be 2 GiB, no? I suggest we drop it (as discussed in the issue).

@danny0838 danny0838 Oct 23, 2026

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It is 4 GiB.

As discussed in the issue, the official hard limit for a local file for Zip64 is 4 GiB. I use "mostly" rather than "that is" because there are still other less common cases, such as > 65535 members, but it would be too verbose to mention all of them here.

decryption of encrypted files in ZIP archives, but it cannot
create an encrypted file. Decryption is extremely slow as it is
implemented in native Python rather than C.
Expand Down Expand Up @@ -204,10 +204,12 @@ ZipFile objects
(:mod:`zlib`, :mod:`bz2`, :mod:`lzma`, or :mod:`compression.zstd`) is not
available, :exc:`RuntimeError` is raised. The default is :const:`ZIP_STORED`.

If *allowZip64* is ``True`` (the default) zipfile will create ZIP files that
use the ZIP64 extensions when the zipfile is larger than 4 GiB. If it is
``false`` :mod:`!zipfile` will raise an exception when the ZIP file would
require ZIP64 extensions.
If *allowZip64* is ``True`` (the default), ZIP64 extensions will be used
on demand when the archive is written, such as when the total archive or an
individual member is larger than 2 GiB (for compatibility with legacy tools
even though the official hard limit is 4 GiB), or when there are more than
65535 members in the archive. If it is ``False``, an exception will be
raised instead.
Comment on lines +207 to +212

@StanFromIreland StanFromIreland Oct 23, 2026

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Suggested change
If *allowZip64* is ``True`` (the default), ZIP64 extensions will be used
on demand when the archive is written, such as when the total archive or an
individual member is larger than 2 GiB (for compatibility with legacy tools
even though the official hard limit is 4 GiB), or when there are more than
65535 members in the archive. If it is ``False``, an exception will be
raised instead.
If *allowZip64* is ``True`` (the default), ZIP64 extensions are used when
needed, such as when a member or the archive reaches 2 GiB or the archive
has more than 65535 members. If it is ``False``, :exc:`LargeZipFile` is
raised instead. When writing a member with :meth:`open`, pass
*force_zip64* if it may reach 2 GiB.

I suggest a few little changes, dropping unnecessary details, clarifying the exception, and noting what happens with open.

@danny0838 danny0838 Oct 23, 2026

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I would argue that "2 GiB threshold is for compatibility rather than official hard limit" is NOT an unnecessary detail. The developer may be confused and the current threshold may be suspected to be incorrectly assigned if this is not explicitly documented.

The details about open is unnecessary since it's already clearly described at ZipFile.open.


The *compresslevel* parameter controls the compression level to use when
writing files to the archive.
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