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brettcannonbrettcannon
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Issue #18810: Be optimistic with stat calls when seeing if a directory
exists when checking for a package. Before there was an isdir check and then various isfile checks for possible __init__ files when looking for a package. This change drops the isdir check by leaning on the assumption that a directory will not contain something named after the module being imported which is not a directory. If the module is a package then it saves a stat call. If there is nothing in the directory with the potential package name it also saves a stat call. Only if there is something in the directory named the same thing as the potential package will the number of stat calls increase (due to more wasteful __init__ checks). Semantically there is no change as the isdir check moved down so that namespace packages continue to have no chance of accidentally collecting non-existent directories.
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2 files changed

Lines changed: 777 additions & 779 deletions

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‎Lib/importlib/_bootstrap.py‎

Lines changed: 9 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1406,16 +1406,15 @@ def find_loader(self, fullname):
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# Check if the module is the name of a directory (and thus a package).
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if cache_module in cache:
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base_path = _path_join(self.path, tail_module)
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if _path_isdir(base_path):
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for suffix, loader in self._loaders:
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init_filename = '__init__' + suffix
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full_path = _path_join(base_path, init_filename)
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if _path_isfile(full_path):
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return (loader(fullname, full_path), [base_path])
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else:
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# A namespace package, return the path if we don't also
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# find a module in the next section.
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is_namespace = True
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for suffix, loader in self._loaders:
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init_filename = '__init__' + suffix
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full_path = _path_join(base_path, init_filename)
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if _path_isfile(full_path):
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return (loader(fullname, full_path), [base_path])
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else:
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# If a namespace package, return the path if we don't
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# find a module in the next section.
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is_namespace = _path_isdir(base_path)
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# Check for a file w/ a proper suffix exists.
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for suffix, loader in self._loaders:
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full_path = _path_join(self.path, tail_module + suffix)

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