[Python] camel case to (fat) snake case

camel_case_to_snake_case.py

def camel_case_to_snake_case(s: str, use_fat: bool = False) -> str:
    """
    >>> camel_case_to_snake_case("ProcedureContextStatus")
    "procedure_context_status"
    >>> camel_case_to_snake_case("ProcedureContextStatus", use_fat=True)
    "PROCEDURE_CONTEXT_STATUS"
    """
    chars = [s[0].upper() if use_fat else s[0].lower()]
    for c in s[1:]:
        if c in ('ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
            chars.append('_')
        chars.append(c.upper() if use_fat else c.lower())
    return ''.join(chars)