[New-bugs-announce] [issue42836] docs: struct: clarify struct caching behaviour
report at bugs.python.org
Wed Jan 6 04:05:31 EST 2021
New submission from Sandeep Subramanian <sandeep at mercari.com>:
As per docs in :https://docs.python.org/3.7/library/struct.html#struct.Struct
> The compiled versions of the most recent format strings passed to Struct and the module-level functions are cached, so programs that use only a few format strings needn’t worry about reusing a single Struct instance.
This statement seems to imply that the format string passed as `struct.Struct(format)` is also cached. This doesn't appear to be the case.
Only format strings passed to the module level functions seems to be cached.
`cache_struct_converter` at https://github.com/python/cpython/blob/v3.7.7/Modules/_struct.c#L2052
appears to be used only in the top module level functions `pack` and `pack_into` and is *not* used in `Struct.__init__`.
Would it be better to change the doc to:
> The compiled versions of the most recent format strings passed to the module-level functions are cached, so programs that use only a few format strings needn’t worry about reusing a single Struct instance.
This issue was introduced by https://github.com/python/cpython/commit/3666b3c1f695a145adab1bf644c22e564e8eb0ee
and is present in every version since.
assignee: docs at python
nosy: docs at python, sandeep2
title: docs: struct: clarify struct caching behaviour
versions: Python 3.10, Python 3.7, Python 3.8, Python 3.9
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