[Python-checkins] cpython: Issue #18810: Be optimistic with stat calls when seeing if a directory

[brett.cannon]

http://hg.python.org/cpython/rev/11f2f4af1979
changeset:   86444:11f2f4af1979
user:        Brett Cannon <brett at python.org>
date:        Fri Oct 18 13:24:13 2013 -0400
summary:
  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.

files:
  Lib/importlib/_bootstrap.py |    19 +-
  Python/importlib.h          |  1537 +++++++++++-----------
  2 files changed, 777 insertions(+), 779 deletions(-)


diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
--- a/Lib/importlib/_bootstrap.py
+++ b/Lib/importlib/_bootstrap.py
@@ -1406,16 +1406,15 @@
         # Check if the module is the name of a directory (and thus a package).
         if cache_module in cache:
             base_path = _path_join(self.path, tail_module)
-            if _path_isdir(base_path):
-                for suffix, loader in self._loaders:
-                    init_filename = '__init__' + suffix
-                    full_path = _path_join(base_path, init_filename)
-                    if _path_isfile(full_path):
-                        return (loader(fullname, full_path), [base_path])
-                else:
-                    # A namespace package, return the path if we don't also
-                    #  find a module in the next section.
-                    is_namespace = True
+            for suffix, loader in self._loaders:
+                init_filename = '__init__' + suffix
+                full_path = _path_join(base_path, init_filename)
+                if _path_isfile(full_path):
+                    return (loader(fullname, full_path), [base_path])
+            else:
+                # If a namespace package, return the path if we don't
+                #  find a module in the next section.
+                is_namespace = _path_isdir(base_path)
         # Check for a file w/ a proper suffix exists.
         for suffix, loader in self._loaders:
             full_path = _path_join(self.path, tail_module + suffix)
diff --git a/Python/importlib.h b/Python/importlib.h
--- a/Python/importlib.h
+++ b/Python/importlib.h
[stripped]

-- 
Repository URL: http://hg.python.org/cpython