1.os.walk(top, topdown=True, οnerrοr=None, followlinks=False)Generate the file names in a directory tree by walking the tree either top-down or bottom-up. For each directory in the tree rooted at directory top (including top itself), it yields a 3-tuple (dirpath, dirnames, filenames).dirpath is a string, the path to the directory. dirnames is a list of the names of the subdirectories in dirpath (excluding '.' and '..'). filenames is a list of the names of the non-directory files in dirpath. Note that the names in the lists contain no path components. To get a full path (which begins with top) to a file or directory in dirpath, do os.path.join(dirpath, name).If optional argument topdown is True or not specified, the triple for a directory is generated before the triples for any of its subdirectories (directories are generated top-down). If topdown is False, the triple for a directory is generated after the triples for all of its subdirectories (directories are generated bottom-up).When topdown is True, the caller can modify the dirnames list in-place (perhaps using del or slice assignment), and walk() will only recurse into the subdirectories whose names remain in dirnames; this can be used to prune the search, impose a specific order of visiting, or even to inform walk() about directories the caller creates or renames before it resumes walk() again. Modifying dirnames when topdown is False is ineffective, because in bottom-up mode the directories in dirnames are generated before dirpath itself is generated.By default, errors from the listdir() call are ignored. If optional argument onerror is specified, it should be a function; it will be called with one argument, an OSError instance. It can report the error to continue with the walk, or raise the exception to abort the walk. Note that the filename is available as the filename attribute of the exception object.By default, walk() will not walk down into symbolic links that resolve to directories. Set followlinks to True to visit directories pointed to by symlinks, on systems that support them.

实例：

This example displays the number of bytes taken by non-directory files in each directory under the starting directory, except that it doesn’t look under any CVS subdirectory:import osfrom os.path import join, getsizefor root, dirs, files in os.walk('python/Lib/email'):    print root, "consumes",    print sum(getsize(join(root, name)) for name in files),    print "bytes in", len(files), "non-directory files"    if 'CVS' in dirs:        dirs.remove('CVS')  # don't visit CVS directoriesIn the next example, walking the tree bottom-up is essential: rmdir() doesn’t allow deleting a directory before the directory is empty:# Delete everything reachable from the directory named in "top",# assuming there are no symbolic links.# CAUTION:  This is dangerous!  For example, if top == '/', it# could delete all your disk files.import osfor root, dirs, files in os.walk(top, topdown=False):    for name in files:        os.remove(os.path.join(root, name))    for name in dirs:        os.rmdir(os.path.join(root, name))