https://www.youtube.com/watch?v=rBfzZdY5BR4

youtube_banner_downloader.py

# Imports
import re
import requests
import sys
import time

# Constants
YOUTUBE_HEADER_IMAGE_START_URL: str = "yt3.ggpht.com/"
YOUTUBE_HEADER_IMAGE_END_URL: str = "-no-nd-rj"

# Get username of requested channel
youtube_username: str = ""
if sys.argv.__len__() <= 1:
  print("no username provided!"); exit(1)
else:
  youtube_username = sys.argv[1]

# Get HTML source of requested channel
start = time.time() # Measure time taken to perform action

channel = requests.get("https://www.youtube.com/{}".format(youtube_username))

if channel.status_code == 404:
  print("channel does not exist"); exit(1)

html: str = channel.text
print("got html source of channel {} in {} seconds".format(youtube_username, time.time() - start))

# RegEx parse HTML source for valid media URLs
start = time.time() # Measure time taken to perform action

# https://stackoverflow.com/questions/23918996/youtube-channel-banner-image-url/64306688#64306688
pattern = re.compile(YOUTUBE_HEADER_IMAGE_START_URL + "(.*?)" + YOUTUBE_HEADER_IMAGE_END_URL, flags=re.DOTALL)
for match in re.finditer(pattern, html):
  image_url = match.group(1)
  if image_url.__len__() < 500:
      print("https://" + YOUTUBE_HEADER_IMAGE_START_URL + image_url + YOUTUBE_HEADER_IMAGE_END_URL)

print("completed regex search of channel {} in {} seconds".format(youtube_username, time.time() - start))