How can I traverse a file system with a generator?

Question

I'm trying to create a utility class for traversing all the files in a directory, including those within subdirectories and sub-subdirectories. I tried to use a generator because generators are cool; however, I hit a snag.

def grab_files(directory):
    for name in os.listdir(directory):
        full_path = os.path.join(directory, name)
        if os.path.isdir(full_path):
            yield grab_files(full_path)
        elif os.path.isfile(full_path):
            yield full_path
        else:
            print('Unidentified name %s. It could be a symbolic link' % full_path)

When the generator reaches a directory, it simply yields the memory location of the new generator; it doesn't give me the contents of the directory.

How can I make the generator yield the contents of the directory instead of a new generator?

If there's already a simple library function to recursively list all the files in a directory structure, tell me about it. I don't intend to replicate a library function.

Answer 1

Why reinvent the wheel when you can use os.walk

import os
for root, dirs, files in os.walk(path):
    for name in files:
        print os.path.join(root, name)

os.walk is a generator that yields the file names in a directory tree by walking the tree either top-down or bottom-up

Answer 2

I agree with the os.walk solution

For pure pedantic purpose, try iterate over the generator object, instead of returning it directly:

def grab_files(directory):
    for name in os.listdir(directory):
        full_path = os.path.join(directory, name)
        if os.path.isdir(full_path):
            for entry in grab_files(full_path):
                yield entry
        elif os.path.isfile(full_path):
            yield full_path
        else:
            print('Unidentified name %s. It could be a symbolic link' % full_path)

Answer 3

As of Python 3.4, you can use the glob() method from the built-in pathlib module:

import pathlib
p = pathlib.Path('.')
list(p.glob('**/*'))    # lists all files recursively

Answer 4

Starting with Python 3.4, you can use the Pathlib module:

In [48]: def alliter(p):
   ....:     yield p
   ....:     for sub in p.iterdir():
   ....:         if sub.is_dir():
   ....:             yield from alliter(sub)
   ....:         else:
   ....:             yield sub
   ....:             

In [49]: g = alliter(pathlib.Path("."))                                                                                                                                                              

In [50]: [next(g) for _ in range(10)]
Out[50]: 
[PosixPath('.'),
 PosixPath('.pypirc'),
 PosixPath('.python_history'),
 PosixPath('lshw'),
 PosixPath('.gstreamer-0.10'),
 PosixPath('.gstreamer-0.10/registry.x86_64.bin'),
 PosixPath('.gconf'),
 PosixPath('.gconf/apps'),
 PosixPath('.gconf/apps/gnome-terminal'),
 PosixPath('.gconf/apps/gnome-terminal/%gconf.xml')]

This is essential the object-oriented version of sjthebats answer. Note that the Path.glob ** pattern returns only directories!

Answer 5

You can use path.py. Unfortunately the author's website is no longer around, but you can still download the code from PyPI. This library is a wrapper around path functions in the os module.

path.py provides a walkfiles() method which returns a generator iterating recursively over all files in the directory:

>>> from path import path
>>> print path.walkfiles.__doc__
 D.walkfiles() -> iterator over files in D, recursively.

        The optional argument, pattern, limits the results to files
        with names that match the pattern.  For example,
        mydir.walkfiles('*.tmp') yields only files with the .tmp
        extension.

>>> p = path('/tmp')
>>> p.walkfiles()
<generator object walkfiles at 0x8ca75a4>
>>> 

Answer 6

addendum to the answer of gerrit. I wanted to make something more flexible.

list all files in pth matching a given pattern, can also list dirs if only_file is False

from pathlib import Path

def walk(pth=Path('.'), pattern='*', only_file=True) :
    """ list all files in pth matching a given pattern, can also list dirs if only_file is False """
    if pth.match(pattern) and not (only_file and pth.is_dir()) :
        yield pth
    for sub in pth.iterdir():
        if sub.is_dir():
            yield from walk(sub, pattern, only_file)
        else:
            if sub.match(pattern) :
                yield sub