Implementation of the global statement

[Terry Reedy]

tem.py:

y=0
def f():
  global y
  y+=1

"Mikael Olofsson" <mikael at isy.liu.se> wrote in message
news:mailman.1038409397.2506.python-list at python.org...

>I have a few related questions. Assume that we have defined f as
above
>in one global namespace, A say, and assume that f (re)binds y. Then
we
>place f in another global namespace, B say. What happens when we
execute
>f in B is that y in A is rebound. I would have guessed that a
variable y
>in B would have been created or rebound. Now to my questions:

>  Why is that so?

Lets augment tem.py with

import math
def g:
  return [f(), math.sin(.033)]

Now your question becomes: why does g look for f and math in tem.py.
Fairly obvious.  Otherwise, doc for g would need to say: 'to run g,
you must define f() and import math.'  Remember, func only has *1*
global context.

>  Is that behaviour intended?
yes
>  Is it likely to stay that way?
yes

>  Is there an obvous way to have f (still defined in A) manipulate
>  objects in B when executed in B?

A way:
>>> import tem
>>> y=0
>>> f=tem.f
>>> tem.f(); y, tem.y
(0, 1)
>>> f(); y, tem.y
(0, 2)
>>> exec tem.f.func_code in globals(); y, tem.y
(1, 2)

eval(tem.f()) or eval(f()) does not change behavior because globals
only affects lookup of tem or f.

Terry J. Reedy