Retrieve filetype:pdf from library

Question

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'):
            books.append(path)
        if os.path.isdir(path):
            walk(path)
def main():
    dir = '~/Documents/MyLibrary/'
    global books
    books = []
    walk(dir)
    print(books)

if __name__ == "__main__":
    main()

Answer 1

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)
    print(books)

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'))
    print(books)

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

Answer 2

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))
        ]
        book_list.append(books)
    return book_list