patch [ 1105730 ] Faster commonprefix in macpath, ntpath, etc.

5 files changed, 35 insertions, 41 deletions

diff --git a/Lib/macpath.py b/Lib/macpath.py
index f50f660..dc7f753 100644
--- a/Lib/macpath.py
+++ b/Lib/macpath.py
@@ -175,14 +175,14 @@ def lexists(path):
 def commonprefix(m):
     "Given a list of pathnames, returns the longest common leading component"
     if not m: return ''
-    prefix = m[0]
-    for item in m:
-        for i in range(len(prefix)):
-            if prefix[:i+1] != item[:i+1]:
-                prefix = prefix[:i]
-                if i == 0: return ''
-                break
-    return prefix
+    s1 = min(m)
+    s2 = max(m)
+    n = min(len(s1), len(s2))
+    for i in xrange(n):
+        if s1[i] != s2[i]:
+            return s1[:i]
+    return s1[:n]
+
 
 def expandvars(path):
     """Dummy to retain interface-compatibility with other operating systems."""
diff --git a/Lib/ntpath.py b/Lib/ntpath.py
index 649e424..35f266c 100644
--- a/Lib/ntpath.py
+++ b/Lib/ntpath.py
@@ -212,14 +212,13 @@ def dirname(p):
 def commonprefix(m):
     "Given a list of pathnames, returns the longest common leading component"
     if not m: return ''
-    prefix = m[0]
-    for item in m:
-        for i in range(len(prefix)):
-            if prefix[:i+1] != item[:i+1]:
-                prefix = prefix[:i]
-                if i == 0: return ''
-                break
-    return prefix
+    s1 = min(m)
+    s2 = max(m)
+    n = min(len(s1), len(s2))
+    for i in xrange(n):
+        if s1[i] != s2[i]:
+            return s1[:i]
+    return s1[:n]
 
 
 # Get size, mtime, atime of files.
diff --git a/Lib/os2emxpath.py b/Lib/os2emxpath.py
index 4c64324..5b1cb18 100644
--- a/Lib/os2emxpath.py
+++ b/Lib/os2emxpath.py
@@ -173,14 +173,13 @@ def dirname(p):
 def commonprefix(m):
     "Given a list of pathnames, returns the longest common leading component"
     if not m: return ''
-    prefix = m[0]
-    for item in m:
-        for i in range(len(prefix)):
-            if prefix[:i+1] != item[:i+1]:
-                prefix = prefix[:i]
-                if i == 0: return ''
-                break
-    return prefix
+    s1 = min(m)
+    s2 = max(m)
+    n = min(len(s1), len(s2))
+    for i in xrange(n):
+        if s1[i] != s2[i]:
+            return s1[:i]
+    return s1[:n]
 
 
 # Get size, mtime, atime of files.
diff --git a/Lib/plat-riscos/riscospath.py b/Lib/plat-riscos/riscospath.py
index 97b4f65..ea39e60 100644
--- a/Lib/plat-riscos/riscospath.py
+++ b/Lib/plat-riscos/riscospath.py
@@ -168,23 +168,16 @@ def dirname(p):
     return split(p)[0]
 
 
-def commonprefix(ps):
-    """
-  Return the longest prefix of all list elements. Purely string-based; does not
-  separate any path parts. Why am I in os.path?
-  """
-    if len(ps)==0:
-        return ''
-    prefix= ps[0]
-    for p in ps[1:]:
-        prefix= prefix[:len(p)]
-        for i in range(len(prefix)):
-            if prefix[i] <> p[i]:
-                prefix= prefix[:i]
-                if i==0:
-                    return ''
-                break
-    return prefix
+def commonprefix(m):
+    "Given a list of pathnames, returns the longest common leading component"
+    if not m: return ''
+    s1 = min(m)
+    s2 = max(m)
+    n = min(len(s1), len(s2))
+    for i in xrange(n):
+        if s1[i] != s2[i]:
+            return s1[:i]
+    return s1[:n]
 
 
 ## File access functions. Why are we in os.path?
diff --git a/Misc/NEWS b/Misc/NEWS
index ebc9b0d..8a2d504 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -178,6 +178,9 @@ Extension Modules
 Library
 -------
 
+- Patch #1105730: Apply the new implementation of commonprefix in posixpath
+  to ntpath, macpath, os2emxpath and riscospath.
+
 - Fix a problem in Tkinter introduced by SF patch #869468: delete bogus
   __hasattr__ and __delattr__ methods on class Tk that were breaking
   Tkdnd.