SF patch #461781 by Chris Lawrence: os.path.realpath - Resolve symlinks:

   Once upon a time, I put together a little function
   that tries to find the canonical filename for a given
   pathname on POSIX. I've finally gotten around to
   turning it into a proper patch with documentation.
   On non-POSIX, I made it an alias for 'abspath', as
   that's the behavior on POSIX when no symlinks are
   encountered in the path.

   Example:
   >>> os.path.realpath('/usr/bin/X11/X')
   '/usr/X11R6/bin/X'

6 files changed, 41 insertions, 0 deletions

diff --git a/Doc/lib/libposixpath.tex b/Doc/lib/libposixpath.tex
index 658b4ea..9cd1a58 100644
--- a/Doc/lib/libposixpath.tex
+++ b/Doc/lib/libposixpath.tex
@@ -137,6 +137,13 @@ case (use \function{normcase()} for that).  On Windows, it converts
 forward slashes to backward slashes.
 \end{funcdesc}
 
+\begin{funcdesc}{realpath}{path}
+Return the canonical path of the specified filename, eliminating any
+symbolic links encountered in the path.
+Availability:  \UNIX{}.
+\versionadded{2.2}
+\end{funcdesc}
+
 \begin{funcdesc}{samefile}{path1, path2}
 Return true if both pathname arguments refer to the same file or
 directory (as indicated by device number and i-node number).
diff --git a/Lib/dospath.py b/Lib/dospath.py
index 958f9f6..5f60705 100644
--- a/Lib/dospath.py
+++ b/Lib/dospath.py
@@ -330,3 +330,6 @@ def abspath(path):
     if not isabs(path):
         path = join(os.getcwd(), path)
     return normpath(path)
+
+# realpath is a no-op on systems without islink support
+realpath = abspath
diff --git a/Lib/macpath.py b/Lib/macpath.py
index 46ae764..1ef35ef 100644
--- a/Lib/macpath.py
+++ b/Lib/macpath.py
@@ -225,3 +225,6 @@ def abspath(path):
     if not isabs(path):
         path = join(os.getcwd(), path)
     return normpath(path)
+
+# realpath is a no-op on systems without islink support
+realpath = abspath
diff --git a/Lib/ntpath.py b/Lib/ntpath.py
index d55cc7c..a1baf83 100644
--- a/Lib/ntpath.py
+++ b/Lib/ntpath.py
@@ -451,3 +451,6 @@ def abspath(path):
     else:
         path = os.getcwd()
     return normpath(path)
+
+# realpath is a no-op on systems without islink support
+realpath = abspath
diff --git a/Lib/plat-riscos/riscospath.py b/Lib/plat-riscos/riscospath.py
index 32f39ba..8eda834 100644
--- a/Lib/plat-riscos/riscospath.py
+++ b/Lib/plat-riscos/riscospath.py
@@ -315,6 +315,10 @@ def abspath(p):
     return normpath(join(os.getcwd(), p))
 
 
+# realpath is a no-op on systems without islink support
+realpath = abspath
+
+
 # Normalize a path. Only special path element under RISC OS is "^" for "..".
 
 def normpath(p):
diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 6bf40f8..0f6b6a7 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -379,3 +379,24 @@ def abspath(path):
     if not isabs(path):
         path = join(os.getcwd(), path)
     return normpath(path)
+
+
+# Return a canonical path (i.e. the absolute location of a file on the
+# filesystem).
+
+def realpath(filename):
+    """Return the canonical path of the specified filename, eliminating any
+symbolic links encountered in the path."""
+    filename = abspath(filename)
+
+    bits = ['/'] + filename.split('/')[1:]
+    for i in range(2, len(bits)+1):
+        component = join(*bits[0:i])
+        if islink(component):
+            resolved = os.readlink(component)
+            (dir, file) = split(component)
+            resolved = normpath(join(dir, resolved))
+            newpath = join(*([resolved] + bits[i:]))
+            return realpath(newpath)
+        
+    return filename