where dos the default agument live in? local name spaces or gloabal namespaces or else?

[Erik Max Francis]

Matt Gerrans wrote:

> > Side note: you probably don't want a mutable as a function default.
> 
> Why is that?

Because usually when that appears in code it is not what is intended and
is often a bug; it's a FAQ of the kind of "This is behaving totally
strangely, I have no idea what's going on here" issues.

Usually a better pattern for otherwise-mutable defaults is something
like:

	def f(l=None):
	    if l is None:
	        l = [] # this will make a new list each time
	    ...

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 A lambda calculus explorer in Python.