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Commit b19ad11

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GH-119169: Slightly speed up os.walk(topdown=True) (GH-121431)
GH-119186: Slightly speed up `os.walk(topdown=True)` When `os.walk()` traverses into subdirectories in top-down mode, call `os.path.join()` once to add a trailing slash, and use string concatenation thereafter to generate child paths.
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‎Lib/os.py‎

Lines changed: 10 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -417,14 +417,16 @@ def walk(top, topdown=True, onerror=None, followlinks=False):
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# Yield before sub-directory traversal if going top down
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yield top, dirs, nondirs
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# Traverse into sub-directories
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for dirname in reversed(dirs):
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new_path = join(top, dirname)
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# bpo-23605: os.path.islink() is used instead of caching
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# entry.is_symlink() result during the loop on os.scandir() because
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# the caller can replace the directory entry during the "yield"
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# above.
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if followlinks or not islink(new_path):
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stack.append(new_path)
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if dirs:
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prefix = join(top, top[:0]) # Add trailing slash
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for dirname in reversed(dirs):
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new_path = prefix + dirname
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# bpo-23605: os.path.islink() is used instead of caching
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# entry.is_symlink() result during the loop on os.scandir() because
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# the caller can replace the directory entry during the "yield"
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# above.
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if followlinks or not islink(new_path):
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stack.append(new_path)
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else:
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# Yield after sub-directory traversal if going bottom up
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stack.append((top, dirs, nondirs))
Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
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Slightly speed up :func:`os.walk` by calling :func:`os.path.join` less
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often.

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