Re: Can't see variables declared as global in a function

[Gary Herron]

Jacob Davis wrote:

Hi.

I have a hundred lines of code in a module that declare some global
variables inside a function so that those variables can be used by
other functions. I want to import this module so that I can more
easily debug by looking at the value of individual variables. But
when I try to reach these variables, I get a warning that they are not
defined.

I am on an Intel Mac running Leopard 10.5.2, Python 2.5

Here is an example of some code that has the same problem:


#!/usr/bin/env python

global isglobal
isglobal=200

def somefunc():
global from_somefunc
from_somefunc=5

def anotherfunc():
return from_somefunc+30


So during debugging I want to look at the variable from_somefunc

here is my terminal output. I start by looking at dir(), then
run somefunc(), then run anotherfunc(), then I want to look
at from_somefunc but I get a warning:

Yuck, YUCK, YUCK! You are breaking *so* many
good-programming-practices, I hardly know where to start.

First off: A python global is not what you think. There are *no*
program wide globals. There are only module wide globals. Also, the
"global isglobal" is absolutely meaningless as anything declared there
is a (module level) global by definition.

SO...

Your from_somefunc is a global variable in module test_vars, but you are
trying to access it from your main module (the interactive session).
The fact that you did "from test_vars import *" isn't going to fix this,
because at the time you did the import, from_somefunc was not defined ad
so was not imported by the "*".

You could just "import test_vars", and then after calling your function
test_vars.somefunc(), you would find that test_vars.from_somefunc would
be defined.

BUT... DON'T DO THAT! A better way: (It is still slightly dubious,
but it is much more straightforward, and does not use the global statement.)

Define your vars.py module:

isglobal=200
# and nothing else

And from your main program,

import vars
print vars.isglobal # will print 200
vars.from_somefunc = 5 # will define and set a global in vars
print vars.from_somefunc+30 # retrieves a global value from vars

As I said above this is still slightly dubious. Better solutions would
probably involve creating a class with each of your huindred variables
as attributes of the class, or a class, each instance of which has the
hundred variables, or ... whatever. To give you better advice, we'd
have to know more about what problem you are trying to solve.
If you really getters and setters (that's what we might call somefucn
and anotherfunc) then you really should be using a class to contain all
the hundred variables, and define getter/setter methods for them.
Gary Herron

>
Python 2.5 (r25:51918, Sep 19 2006, 08:49:13)
[GCC 4.0.1 (Apple Computer, Inc. build 5341)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

>from test_vars import *
dir()

['__builtins__', '__doc__', '__name__', 'anotherfunc', 'isglobal',
'somefunc']

>somefunc()
anotherfunc()

35

>isglobal

200

>from_somefunc

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'from_somefunc' is not defined

>dir()

['__builtins__', '__doc__', '__name__', 'anotherfunc', 'isglobal',
'somefunc']

Is there a way that I can view from_somefunc?

Thanks,

Jake