Date:         Fri, 18 Aug 2006 17:54:01 +0200
Reply-To:     Georg.Maubach@dpwnbc.net
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Georg Maubach <Georg.Maubach@dpwnbc.net>
Subject:      Visibility of Python Variables
Content-Type: text/plain; charset="us-ascii"

Hi All,

I have a general question on Python programming.

In a function variables need to be declared as global if I wanna use a
variable in the function that was defined outside the function. But if I
use it as a parameter to a function this is not necessary.

I include a simple script code explaining the question in more detail.

--------------------- cut --------------------

# Author: Georg Maubach
# Date  : 16-Aug-2006
# File  : VisibilityOfVariables.py

from turtle import *

width(10)

step = 100 # a global variable is defined
color("blue")

# Section 1: Code works
def triangle():
    forward(step) # The global variable step which should not be visible
to the
    left(120)     # interpreter does not cause an error during program
run
    forward(step) # although it should be addressable by the interpreter
    left(120)     # cause the global variable "step" was not introduced
to the
    forward(step) # function "triangle" by using "global step".
    left(120)     # Why does this not raise an error?


triangle()

# Section 2: Code does not work
def rectangle():
    forward(step)
    left(90)
    forward(step)
    left(90)
    forward(step)
    left(90)
    forward(step)
    left(90)
    step = step + change # Why does this not work? The variable was
                         # defined as before. Now it seems to be not
                         # visible. Why? What is the difference between
                         # Section 1 and 2?
    left(60) # next rectangle


rectangle()

# eof #

--------------------- cut --------------------

The question is why do I have not to declare a global variable to be
used as function parameter whereas I have to declare this variable as
global if I want to assign another value?

Question to List-Owner:
My question is more general. Is it off-topic to ask these questions on
this list?

I am looking forward to hearing from you.

Best regards

Georg Maubach
Market Analyst