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GH-119169: Slightly speed up os.walk(topdown=True) #121431

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GH-119169: Slightly speed up os.walk(topdown=True) #121431

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GH-119186: Slightly speed up `os.walk(topdown=True)`
barneygale Jul 6, 2024
6534a36
Merge branch 'main' into gh-119186-joining
barneygale Jul 8, 2024
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18 changes: 10 additions & 8 deletions Lib/os.py
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Original file line number Diff line number Diff line change
Expand Up @@ -416,14 +416,16 @@ def walk(top, topdown=True, onerror=None, followlinks=False):
# Yield before sub-directory traversal if going top down
yield top, dirs, nondirs
# Traverse into sub-directories
for dirname in reversed(dirs):
new_path = join(top, dirname)
# bpo-23605: os.path.islink() is used instead of caching
# entry.is_symlink() result during the loop on os.scandir() because
# the caller can replace the directory entry during the "yield"
# above.
if followlinks or not islink(new_path):
stack.append(new_path)
if dirs:
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How much of the gain is due to the elimination of os.join and how much due to the check on empty dirs? On my system a walk of a folder with github repositories (including the cpython repo) has dirs empty about 60% of the times.

prefix = join(top, top[:0]) # Add trailing slash
for dirname in reversed(dirs):
new_path = prefix + dirname
# bpo-23605: os.path.islink() is used instead of caching
# entry.is_symlink() result during the loop on os.scandir() because
# the caller can replace the directory entry during the "yield"
# above.
if followlinks or not islink(new_path):
stack.append(new_path)
else:
# Yield after sub-directory traversal if going bottom up
stack.append((top, dirs, nondirs))
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2024-07-06-14-32-30.gh-issue-119186.E5B1HQ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Slightly speed up :func:`os.walk` by calling :func:`os.path.join` less
often.
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