Bug report

Bug description:

SectionProxy and RawConfigParser inherit clear() from MutableMapping, which calls popitem() once per entry. Each popitem() call copies all remaining keys (SectionProxy.__iter__() builds the merged option list, RawConfigParser.popitem() calls sections()), so clearing a section or the parser takes quadratic time.

import configparser, time
cp = configparser.RawConfigParser()
cp.read_string("[s]\n" + "".join(f"k{i} = v\n" for i in range(20000)))
t = time.perf_counter(); cp["s"].clear(); print(time.perf_counter() - t)

This takes several seconds for 20000 options and four times as long with twice as many; parser.clear() with many sections behaves the same way. parser.clear() dates from gh-61024.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-161108: Make configparser clear() linear time #161109
• [3.14] gh-161108: Make configparser clear() linear time (GH-161109) #161133
• [3.15] gh-161108: Make configparser clear() linear time (GH-161109) #161134