[Tutor] Question about global variables on modules

[Dave Kuhlman]

On Fri, Apr 04, 2008 at 10:25:30PM -0300, Tiago Katcipis wrote:
> I know its not such a pretty thing to have global variables but its only
> for an exercise my teacher told to do. Its a function to calculate the
> results of a matrix using jacob. I want to inside the module (inside a
> function on the module )assign a value to a global variable, but the
> only way i found to do this inside the own module function is importing
> the module inside himself. Is there another way of doing this? its kind
> odd to import the module to himself, i think :-)

If you want to assign a value to a global variable from within a
function, use the global statement.  Examples:

    A_GLOBAL_VALUE = 0

    # Example: assign value to local variable
    def t1():
        a_value = 4
        return a_value * 3

    # Example: assign value to global variable
    def t2():
        global A_GLOBAL_VALUE
        A_GLOBAL_VALUE = 4
        return a_value * 3

    # Example: get (but do not set) the value of a global variable
    def t3():
        a_value = A_GLOBAL_VALUE
        print a_value

    def test():
        print t1()
        print t2()
        print A_GLOBAL_VALUE
        print t3()

    test()

See http://docs.python.org/ref/global.html.

Note that to *get* (not set) the value of a global variable from
within a function, you do not need to use the global statement.

- Dave


-- 
Dave Kuhlman
http://www.rexx.com/~dkuhlman