> if the call occurs in the function signature, it doesn't really make sense that the call would somehow happen again and again. You're not defining a function

> if the call occurs in the function signature, it doesn't really make sense that the call would somehow happen again and again. You're not defining a function in the signature; you're specifying a value right there. There are things besides functions and values! They're called "expressions" or "code blocks", and in an impure language like Python they can produce a different value each time you evaluate them. In my second example, "Person()" is neither a value nor a function -- it's an expression that would be evaluated each time the function is run. This isn't that weird; in `while condition: body`, `body` is a block that's evaluated multiple times. It would need to capture variables from the local environment though, which makes it more complicated to implement. > The current PEP proposal is to enable the "evaluate at function call time" ability with new syntax, which I think makes the most sense semantically and also doesn't break existing code. Oh yeah I wasn't suggesting breaking existing code. Just that if I was designing a language from scratch, it would probably avoid the Python foot-gun and have default arguments evaluated each time.