I retrieved all the books in pdf from my library with a recursive function.

import os

def walk(dirname):
    for name in os.listdir(dirname):
        path = os.path.join(dirname, name)

        if os.path.isfile(path) and path.endswith('pdf'):
        if os.path.isdir(path):
def main():
    dir = '~/Documents/MyLibrary/'
    global books
    books = []

if __name__ == "__main__":

Similarly to a feature in most UNIX shells, Python has a globbing module, called glob.

It even supports the extended globbing (using ** to recursively descend into sub-folders) since Python 3.5, which you can use like this:

import os
from glob import glob

if __name__ == "__main__":
    dir = os.path.expanduser('~/Documents/MyLibrary/')
    books = glob(os.path.join(dir, "**/*.pdf"), recursive=True)

Here I also used the os.path module to correctly join the paths and expand the ~ symbol to the users home directory.

Alternatively, you could use the pathlib.Path object (introduced in Python 3.4), which also supports globbing:

from pathlib import Path

if __name__ == "__main__":
    dir = Path('~/Documents/MyLibrary/').expanduser()
    books = list(dir.glob('**/*.pdf'))

Note the list call, which is necessary, because the Path.glob method returns a generator (in contrast to glob.glob, which returns a list).

  • \$\begingroup\$ This is a solution I dare not to imagine, surprise :> \$\endgroup\$ – AbstProcDo Jan 2 '18 at 12:41

You are essentially imitating the behaviour of os.walk function, which is already present in python.

Here is a minor implementation of fnmatch to filter out a glob-based file-pattern from the os.walk's result. Since, you do not need an exclude section, your implementation would be easier. Although, personally; I'd go with .endswith check as it is easier to read (and more pythonic).

More importantly, using global variable is a very bad design practice and must be avoided. You can define a new function get_files_of_type, which takes a parameter of type of files to filter out, and another parameter for the source path, and simply returns the list generated after os.walk. A rough implementation would look like (untested):

def get_files_of_types(path='.', file_types=None):
    path: string depicting the path which is to be walked
    file_types: list of extensions to be checked against
    if file_types is None:
        file_types = ['pdf']
    book_list = []
    for root, sub_dirs, files in os.walk(path):
        books = [
            os.path.join(root, f)
            for f in files if f.endswith(tuple(file_types))
    return book_list
  • \$\begingroup\$ How about using os.path.splitext instead of str.endswith? \$\endgroup\$ – Daniel Jan 2 '18 at 12:21
  • 1
    \$\begingroup\$ @Coal_ with .endswith, a user may chose to provide either .pdf or pdf. \$\endgroup\$ – hjpotter92 Jan 2 '18 at 12:24
  • 1
    \$\begingroup\$ A docstring would be really helpful for this method, because get_files_of_type(".", ".pdf") would produce interesting results (since tuple will be called on file_types, it produces ('.', 'p', 'd', 'f')). \$\endgroup\$ – Graipher Jan 2 '18 at 12:56
  • 2
    \$\begingroup\$ Also, I would call it get_files_of_types to make it clearer that an iterable of types must be supplied. \$\endgroup\$ – Graipher Jan 2 '18 at 13:23

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