[Python-ideas] Symlink chain resolver module

[Giampaolo Rodola']

Hi there,
I thought it would have been good sharing this code I used in a
project of mine.
I thought it could eventually look good incorporated in Python stdlib
through os or os.path modules.
Otherwise I'm merely offering it as a community service to anyone who
might be interested.


-- Giampaolo


#!/usr/bin/env python
# linkchainresolver.py

import os, sys, errno

def resolvelinkchain(path):
    """Resolve a chain of symbolic links by returning the absolute
path
    name of the final target.

    Raise os.error exception in case of circular link.
    Do not raise exception if the symlink is broken (pointing to a
    non-existent path).
    Return a normalized absolutized version of the pathname if it is
    not a symbolic link.

    Examples:

    >>> resolvelinkchain('validlink')
    /abstarget
    >>> resolvelinkchain('brokenlink') # resolved anyway
    /abstarget
    >>> resolvelinkchain('circularlink')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "module.py", line 19, in resolvelinkchain
        os.stat(path)
    OSError: [Errno 40] Too many levels of symbolic links: '3'
    >>>
    """
    try:
        os.stat(path)
    except os.error, err:
        # do not raise exception in case of broken symlink;
        # we want to know the final target anyway
        if err.errno == errno.ENOENT:
            pass
        else:
            raise
    if not os.path.isabs(path):
        basedir = os.path.dirname(os.path.abspath(path))
    else:
        basedir = os.path.dirname(path)
    p = path
    while os.path.islink(p):
        p = os.readlink(p)
        if not os.path.isabs(p):
            p = os.path.join(basedir, p)
            basedir = os.path.dirname(p)
    return os.path.join(basedir, p)