list or get python source files using requests_html

"""
This script list or download Python source files
It was requested here: https://python-forum.io/Thread-downloading-source-for-every-version

Dependencies: requests, requests_html
Task: Remove external dependencies
"""


import re
import sys
try:
    import requests
    import requests_html
except ImportError:
    print('Please install requests and requests_html.', file=sys.stdout)
    sys.exit(255)


def sorter(url):
    """
    This sorter is used to sort the
    python by version string.

    Early version have only two digits.
    """
    v1 = re.search(r'(\d+)\.(\d+)\.(\d+)', url)
    v2 = re.search(r'(\d+)\.(\d+)', url)
    if v1:
        return tuple(map(int, v1.groups()))
    elif v2:
        return tuple(map(int, [*v2.groups(), 0]))
    else:
        return (0,0,0)


def get_python_sources(filetype='tgz'):
    """
    Grab all links from python.org/downloads/source/
    Return the source file archives sorted as a list.
    """
    url = 'https://www.python.org/downloads/source/'
    with requests_html.HTMLSession() as session:
        req = session.get(url)
    links = [link for link in req.html.links if link.endswith(filetype)]
    return sorted(links, key=sorter)


def print_python_sources():
    """
    Print all python source links to stdout.
    """
    for link in get_python_sources():
        print(link)


def download_python_sources():
    """
    Download all python source files to current location.
    """
    for link in get_python_sources():
        file = link.split('/')[-1]
        # find a better way to get the file name from url
        # maybe urllib.parse?
        # yarl is an alternative with more abstraction
        print('Downloading', file)
        req = requests.get(link, stream=True)
        with open(file, 'wb') as fd:
            for chunk in req.iter_content(chunk_size=64*1024**1):
                # what is the ideal chunk_size?
                # how to detect the best chunk_size?
                fd.write(chunk)


def help():
    print('python3', sys.argv[0], '<list|download>')
    sys.exit(1)


if __name__ == '__main__':
    if len(sys.argv) != 2:
        help()
    cmd = sys.argv[1].lower()
    if cmd not in ('download', 'list'):
        help()
    try:
        if cmd == 'list':
            print_python_sources()
        elif cmd == 'download':
            download_python_sources()
    except Exception as e:
        # catching all exceptions here, the're bubbleing up
        # extend this to handle different cases
        print('Error:', e)