python - How to define default argument value based on previous arguments?

Question

I want to define a resize(h, w) method, and I want to be able to call it in one of two ways:

1. resize(x,y)
2. resize(x)

Where, in the second call, I want y to be equal to x. Can I do this in the method definition or should I do something like resize(x,y=None) and check inside:

if y is None:
    y = x

Answer 1

Can I do this in the method definition

No. During the method definition there's no way to know what value x might have at run-time. Default arguments are evaluated once at definition time, there's no way to save a dynamic value for y.

or should I do something like resize(x,y=None) and check inside

exactly. This is a common idiom in Python.