Question

I want to write a function that has a default value that is another input of the function. I’d like something like this:

def pythag_thm(a, b=a):
    return (a**2 + b**2)**.5

but I get a NameError: name 'a' is not defined. I realize I could do something like:

def pythag_thm(a, b=False):
     if b==False:
         return (a**2 + a**2)**.5
     else:
         return (a**2 + b**2)**.5

but this does not seem very ‘pythonic’. Is there a clean way to do this? Am I just thinking of this in the wrong way?

Answer 1

What people usually do is

def pythag_thm(a, b=None):
    if b is None:
        b = a

    return (a ** 2 + b ** 2) ** .5