why in express 3 was used the built-in favicon, and in express 4 external? code example

Example 1: "http://" looks like a URL. Beautiful Soup is not an HTTP client. You should probably use an HTTP client like requests to get the document behind the URL, and feed that document to Beautiful Soup. markup

import warnings
warnings.filterwarnings("ignore", category=UserWarning, module='bs4')

Example 2: what is the function prototype for fgetc()

int fgetc(FILE *filename);