On Sat, 03 Nov 2007 07:18:17 +0000, Sullivan WxPyQtKinter wrote:
> I am confused by the following program:
>
> def f():
> print x
> x=12345
> f()
>
> result is:
>>>>
> 12345
If python can't discover x in your current scope and you do not bind to
it there, it will automatically access that global name x.
> however:
> def f():
> print x
> x=0
>
> x=12345
> f()
>
> result is:
> Traceback (most recent call last):
> File "...\test.py", line 5, in ?
> f()
> File "...\test.py", line 2, in f
> print x
> UnboundLocalError: local variable 'x' referenced before assignment
Here, you *do* assign to x in this scope so this is essentially the same
as the following (without any function scope)::
print x
x = 12345
This can't work since you haven't used x when you try to print it.
You can make this work using the `global` statement::
>>> def foo():
... global x
... print x
... x = 0
...
>>> x = 12345
>>> print x
12345
>>> foo()
12345
>>> print x
0
See more in the `lexical reference about the global statement <http://
docs.python.org/ref/global.html>.
HTH,
Stargaming
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