On Sun, 11 May 2014 11:59:21 +1000, Chris Angelico wrote:
> On Sun, May 11, 2014 at 11:28 AM, Ethan Furman <et...@stoneleaf.us>
> wrote:
>> Well, with function variables they have to exist *when you use them*.
>> ;)
>>
>> This seems like more of a scoping issue than a "can we create variables
>> in Python" issue.
>>
>> I am curious, though, what other python's do with respect to function
>> variables.
>
> Variables exist in scope. Apart from assembly language, where registers
> have universal scope, every language I know of has some concept of
> scope.
BASIC.
> (REXX is very different from most, in that "PROCEDURE EXPOSE"
> isn't at all your classic notion of scoping, but there's still the
> concept that there can be two variables with the same name.) When you
> create one, you create it in a particular scope, and that's how it must
> be.
Yes. But when do you create it? At declaration time, or when a value is
bound to it?
# Ensure spam does not exist.
try:
del spam
except NameError:
pass
assert "spam" not in globals()
# Declare spam.
global spam
print ("spam" in globals()) # prints False
print (spam) # raises NameError
The same applies to locals. Whether a slot is pre-allocated or not, the
variable doesn't exist until there is a value bound to the name.
--
Steven D'Aprano
http://import-that.dreamwidth.org/
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