Easy questions from a python beginner

[Steven D'Aprano]

On Mon, 12 Jul 2010 09:48:04 +0100, bart.c wrote:

> That's interesting. So in Python, you can't tell what local variables a
> function has just by looking at it's code:

In the presence of "exec", you can't really tell *anything*.

>>> def f(s):
...     exec s
...     print locals()
...
>>> f("x = 2;y = None")
{'y': None, 'x': 2, 's': 'x = 2;y = None'}



 
> def foo(day):
>  if day=="Tuesday":
>   x=0
>  print ("Locals:",locals())
> 
> #foo("Monday")
> 
> Does foo() have 1 or 2 locals? 

That's easy for CPython: it prepares two slots for variables, but only 
creates one:

>>> foo("Monday")
('Locals:', {'day': 'Monday'})
>>> foo.func_code.co_varnames
('day', 'x')
>>> foo.func_code.co_nlocals
2

So, the question is, is x a local variable or not? It's not in locals, 
but the function clearly knows that it could be.


> That might explain some of the
> difficulties of getting Python implementations up to speed.

I'm not quite sure why you say that.


-- 
Steven