def sub(pattern, repl, string, count=<NUM_LIT:0>, flags=<NUM_LIT:0>):
return _compile(pattern, flags).sub(repl, string, count)<EOL>
Return the string obtained by replacing the leftmost
    non-overlapping occurrences of the pattern in string by the
    replacement repl.  repl can be either a string or a callable;
    if a string, backslash escapes in it are processed.  If it is
    a callable, it's passed the match object and must return
    a replacement string to be used.