[Django] #37082: Improved readability and minor performance of sanitize_strftime_format regex substitution

[Django]

#37082: Improved readability and minor performance of sanitize_strftime_format
regex substitution
-------------------------------------+-------------------------------------
Reporter: xMintTea | Type:
| Cleanup/optimization
Status: new | Component: Core
| (Other)
Version: 6.0 | Severity: Normal
Keywords: | Triage Stage:
sanitize_strftime_format, regex, | Unreviewed
readability, performance |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
The current implementation of `sanitize_strftime_format` uses an inline
lambda with indexed groups (`r"%s%%0%s%s" % (m[1], mapping[m[2]], m[2])`)
and a compact regular expression. While correct, it is not immediately
obvious what the replacement does and why the groups are referenced by
index.

This patch replaces the lambda with a small helper function
`_replace_specifier`, uses a named group `(?P<letter>...)` in the regex,
enables `re.VERBOSE` for readability, and switches to an f-string for
clarity.

**No behavioral changes** – the early exit condition and the mapping
dictionary remain identical. Equivalence was verified on Windows by
mocking the early exit and comparing outputs for a comprehensive set of
format strings, including edge cases with escaped percent signs (`%%`).
The regex match results were also confirmed to be the same.

Additionally, the use of an f-string and named group yields a ~12-13%
performance improvement over the old `%`-formatting with `m[1]`/`m[2]`
access (measured with timeit on 240,000 calls).
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Ticket URL: <https://code.djangoproject.com/ticket/37082>
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[Django]

#37082: Improved readability and minor performance of sanitize_strftime_format
regex substitution
-------------------------------------+-------------------------------------

Reporter: xMintTea | Owner: (none)
Type: | Status: new
Cleanup/optimization |

Component: Core (Other) | Version: 6.0

Severity: Normal | Resolution:

Keywords: | Triage Stage:
sanitize_strftime_format, regex, | Unreviewed
readability, performance |

Has patch: 1 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Changes (by xMintTea):

* has_patch: 0 => 1

--
Ticket URL: <https://code.djangoproject.com/ticket/37082#comment:1>

[Django]

#37082: Improved readability and minor performance of sanitize_strftime_format
regex substitution
-------------------------------------+-------------------------------------
Reporter: xMintTea | Owner: (none)

Type: | Status: closed

Cleanup/optimization |
Component: Core (Other) | Version: 6.0

Severity: Normal | Resolution: wontfix

Keywords: | Triage Stage:
sanitize_strftime_format, regex, | Unreviewed
readability, performance |

Has patch: 0 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Changes (by Jacob Walls):

* has_patch: 1 => 0
* resolution: => wontfix
* status: new => closed

Comment:

This function is cached.
--
Ticket URL: <https://code.djangoproject.com/ticket/37082#comment:2>