#! /usr/bin/env python # 3)  System Test##     Given a list of directories, report any bogus symbolic links contained#     anywhere in those subtrees.  A bogus symbolic link is one that cannot#     be resolved because it points to a nonexistent or otherwise#     unresolvable file.  Do *not* use an external find executable.#     Directories may be very very deep.  Print a warning immediately if the#     system you're running on doesn't support symbolic links. # This implementation:# - takes one optional argument, using the current directory as default# - uses chdir to increase performance# - sorts the names per directory# - prints output lines of the form "path1 -> path2" as it goes# - prints error messages about directories it can't list or chdir into import osimport sysfrom stat import * def main():    try:        # Note: can't test for presence of lstat -- it's always there        dummy = os.readlink    except AttributeError:        print "This system doesn't have symbolic links"        sys.exit(0)    if sys.argv[1:]:        prefix = sys.argv[1]    else:        prefix = ''    if prefix:        os.chdir(prefix)        if prefix[-1:] != '/': prefix = prefix + '/'        reportboguslinks(prefix)    else:        reportboguslinks('') def reportboguslinks(prefix):    try:        names = os.listdir('.')    except os.error, msg:        print "%s%s: can't list: %s" % (prefix, '.', msg)        return    names.sort()    for name in names:        if name == os.curdir or name == os.pardir:            continue        try:            mode = os.lstat(name)[ST_MODE]        except os.error:            print "%s%s: can't stat: %s" % (prefix, name, msg)            continue        if S_ISLNK(mode):            try:                os.stat(name)            except os.error:                print "%s%s -> %s" % \                      (prefix, name, os.readlink(name))        elif S_ISDIR(mode):            try:                os.chdir(name)            except os.error, msg:                print "%s%s: can't chdir: %s" % \                      (prefix, name, msg)                continue            try:                reportboguslinks(prefix + name + '/')            finally:                os.chdir('..') main()