import re


def is_line_function_definition(line: str) -> bool:
    """Returns true if the corresponding line (of a python file) is the start of a function definition.

    Excludes functions that start with `__` which indicates a private function.

    Args:
        line: a line in a python file
    """
    return bool(re.search('^( *)def ', line)) and 'def __' not in line