如何实现一个函数而不是三个函数？

def my_function(x):
    # 实现功能1
    pass

def my_function(x, y):
    # 实现功能2
    pass

def my_function(x, y, z):
    # 实现功能3
    pass

def my_function(x, y=None, z=None):
    if y is None and z is None:
        # 实现功能1
        pass
    elif y is not None and z is None:
        # 实现功能2
        pass
    elif y is not None and z is not None:
        # 实现功能3
        pass

def my_function(*args):
    if len(args) == 1:
        # 实现功能1
        pass
    elif len(args) == 2:
        # 实现功能2
        pass
    elif len(args) == 3:
        # 实现功能3
        pass