Question about "global" statement

[ChrisWang]

Hi,

I am having trouble understanding the use of 'global' variables I want to use a global variable with the same name as a parameter of a function. But I don't know how to use them at the same time. Here is a snippet of example code:

def foo (a):
    global p
    global a
    p = a + 3  #here "a" will be reference to the global one
    
a = 1
p = 0
foo (a)
print a, p

When I executed this script, Python said "SyntaxErro r: name 'a' is local and global". I don't think there is anything wrong with Python, but just want to find a way to use local and global variable in one function. In CPP, we can use :: prefix to indicate the variable is global. But I have no idea that how to implement it in Python. Could anybody tell me the solution?

Thanks!

[Smygis]

If you have to use global variables my favorite way is to crate a container for the global variables, like this:

>>> class gv: pass
... 
>>> def foo():
...     gv.p = gv.a + 3
... 
>>> gv.p, gv.a = 0, 1
>>> foo()
>>> print gv.a, gv.p
1 4
>>>

Anyway what you are doing wrong is exactly what the error message says. There is two "a" and python gets confused as to whom of them you are referring to.

>>> def bar(a):
...     global a
...     print a
... 
SyntaxError: name 'a' is local and global

Solve it by using different variable names. This is why i prefer to create the container for global variables. Its to keep them separate form the other variables.

[ChrisWang]

Good suggestion! Thanks!

[ChrisWang]

I found another solution to this problem.

I can use a name space for the scoping.

__main__.a will be referenced to a global variable.

Anyway, I think container is better.

[Curtis Rutland]

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