requests: Download file if it doesn't exist

import requests
import os.path

def download_file(filename, url):
    """
    Download an URL to a file
    """
    with open(filename, 'wb') as fout:
        response = requests.get(url, stream=True)
        response.raise_for_status()
        # Write response data to file
        for block in response.iter_content(4096):
            fout.write(block)

def download_if_not_exists(filename, url):
    """
    Download a URL to a file if the file
    does not exist already.

    Returns
    -------
    True if the file was downloaded,
    False if it already existed
    """
    if not os.path.exists(filename):
        download_file(filename, url)
        return True
    return False