How to use youtube-dl from a python program?

It's not difficult and actually documented:

import youtube_dl

ydl = youtube_dl.YoutubeDL({'outtmpl': '%(id)s.%(ext)s'})

with ydl:
    result = ydl.extract_info(
        'http://www.youtube.com/watch?v=BaW_jenozKc',
        download=False # We just want to extract the info
    )

if 'entries' in result:
    # Can be a playlist or a list of videos
    video = result['entries'][0]
else:
    # Just a video
    video = result

print(video)
video_url = video['url']
print(video_url)

For simple code, may be i think

import os
os.system('youtube-dl [OPTIONS] URL [URL...]')

Above is just running command line inside python.

Other is mentioned in the documentation Using youtube-dl on python Here is the way

from __future__ import unicode_literals
import youtube_dl

ydl_opts = {}
with youtube_dl.YoutubeDL(ydl_opts) as ydl:
    ydl.download(['https://www.youtube.com/watch?v=BaW_jenozKc'])

Here is a way.

We set-up options' string, in a list, just as we set-up command line arguments. In this case opts=['-g', 'videoID']. Then, invoke youtube_dl.main(opts). In this way, we write our custom .py module, import youtube_dl and then invoke the main() function.