Importing file names, etc., etc.

import os

def dirEntries(dir_name, subdir, *args):
    '''Return a list of file names found in directory 'dir_name'
    If 'subdir' is True, recursively access subdirectories under 'dir_name'.
    Additional arguments, if any, are file extensions to match filenames.
        Matched file names are added to the list.
    If there are no additional arguments, all files found in the directory
        are added to the list.
    Example usage: fileList = dirEntries(r'H:\TEMP', False, 'txt', 'py')
        Only files with 'txt' and 'py' extensions will be added to the list.
    Example usage: fileList = dirEntries(r'H:\TEMP', True)
        All files and all the files in subdirectories under H:\TEMP will be
        added to the list.
    '''
    fileList = []
    for file in os.listdir(dir_name):
        dirfile = os.path.join(dir_name, file)
        if os.path.isfile(dirfile):
            if not args:
                fileList.append(dirfile)
            else:
                if os.path.splitext(dirfile)[1][1:] in args:
                    fileList.append(dirfile)
        # recursively access file names in subdirectories
        elif os.path.isdir(dirfile) and subdir:
            print "Accessing directory:", dirfile
            fileList.extend(dirEntries(dirfile, subdir, *args))
    return fileList

dirEntries(dir_name, False, 'sac')