Suppose we want to add support for a new parameter name in a function, without removing the old one (rather adding deprecation warning for that)

```
def f(a=2, b=2):
    # we want users to use b, so need to pass deprecation 
    # warning for a when a is used.
    if(b is 2 and a is not 2): # a is used
        warnings.warn("a is deprecated in future update. Please use b")
        # But we miss case when a=2 is passed

```

Please suggest what could be a better way to have this feature. Thanks :)