String cases algorithms for python

case.py

def camel_to_snake(str):
    """
    camelCase to snake_case
    'camelCase' -> 'camel_case'
    """
    return ''.join(map(lambda char:char if char.islower() else "_"+char.lower(), str))


def snake_to_camel(str):
    """
    snake_case to camelCase
    'snake_case' -> 'snakeCase'
    """
    return ''.join(map(lambda char:char if char.islower() else "_"+char.lower(), str))