8000 gh-107369: Optimise ``textwrap.indent()`` by AA-Turner · Pull Request #131923 · python/cpython · GitHub
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gh-107369: Optimise textwrap.indent() #131923

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Merged
merged 1 commit into from
Mar 31, 2025
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gh-107369: Optimise textwrap.indent() #131923

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25 changes: 13 additions & 12 deletions Lib/textwrap.py
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Original file line number Diff line number Diff line change
Expand Up @@ -451,19 +451,20 @@ def indent(text, prefix, predicate=None):
it will default to adding 'prefix' to all non-empty lines that do not
consist solely of whitespace characters.
"""
if predicate is None:
# str.splitlines(True) doesn't produce empty string.
# ''.splitlines(True) => []
# 'foo\n'.splitlines(True) => ['foo\n']
# So we can use just `not s.isspace()` here.
predicate = lambda s: not s.isspace()

prefixed_lines = []
for line in text.splitlines(True):
if predicate(line):
prefixed_lines.append(prefix)
prefixed_lines.append(line)

if predicate is None:
# str.splitlines(keepends=True) doesn't produce the empty string,
# so we need to use `str.isspace()` rather than a truth test.
# Inlining the predicate leads to a ~30% performance improvement.
for line in text.splitlines(True):
if not line.isspace():
prefixed_lines.append(prefix)
prefixed_lines.append(line)
else:
for line in text.splitlines(True):
if predicate(line):
prefixed_lines.append(prefix)
prefixed_lines.append(line)
return ''.join(prefixed_lines)


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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-03-31-02-06-57.gh-issue-107369.8M-HVz.rst
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@@ -0,0 +1,2 @@
Improved performance of :func:`textwrap.dedent` by an average of ~1.3x.
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s/dedent/indent/

Patch by Adam Turner.
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