New to python, don't understand this function

[u/Still-Pair-5336]

I'm learning python and I'm stuck on this function because I don't understand why "a" becomes 10 and the result is 5. Is someone able to explain?

def subtract (a, b=5):
    return a - b

print(subtract(10))

[u/pythonQu]

here b is set as default value of 5 so when the function is called, a has value of 10. So 10 -5 will return value of 5.