bpo-33587: inspect.getsource: reorder stat on file in linecache (GH-6805)

* inspect.getsource: avoid stat on file in linecache

The check for os.path.exists() on source file is postponed in
inspect.getsourcefile() until needed avoiding an expensive filesystem
stat call and PEP 302 module loader check is moved last for performance
since it is an uncommon case.

diff --git a/Lib/inspect.py b/Lib/inspect.py
index cbc0632484b83264dcce14c833347bc6563a16fb..498ee7ab9eaf8a2cfcae08428adfc40e7b2db7db 100644 (file)
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -946,6 +946,9 @@ def getsourcefile(object):
     elif any(filename.endswith(s) for s in
                  importlib.machinery.EXTENSION_SUFFIXES):
         return None
+    # return a filename found in the linecache even if it doesn't exist on disk
+    if filename in linecache.cache:
+        return filename
     if os.path.exists(filename):
         return filename
     # only return a non-existent filename if the module has a PEP 302 loader
@@ -954,9 +957,6 @@ def getsourcefile(object):
         return filename
     elif getattr(getattr(module, "__spec__", None), "loader", None) is not None:
         return filename
-    # or it is in the linecache
-    elif filename in linecache.cache:
-        return filename
 
 def getabsfile(object, _filename=None):
     """Return an absolute path to the source or compiled file for an object.