Guilty secret: globals baffle me

[Dennis Lee Bieber]

Edward K. Ream fed this fish to the penguins on Wednesday 06 November 
2002 06:43 am:


> My questions:
> 
> 1. How many globals are there?  Is there just one, or does each module
> define its own?
>

        In a simplistic sense, globals are names which exist at the top level 
of each module (or .py file, including your "main" program). Locals are 
names which are created/used inside of nested definition levels...

aGlobal = []

def something(arg):
        aLocal = arg

class someitem():       #warning, very loose usage here, likely not runable
        aClassLocal = 1
        def __init__(self, arg):
                aInstanceLocal = arg

> 2. It seems that:
> 
> global foo
> foo = x
> ...
> global
> print foo
> 
> only works if the two parts are within the same module, so I think
> maybe globals() returns module specific stuff, but then why call it
> globals?
> 

        The global statement is needed /inside/ def/class components in order 
to reference the stuff at the module level.

aGlobal1 = []
aGlobal2 = []

def something(arg1, arg2):
        global aGlobal2
        aGlobal1 = arg1 #DOES NOT ACCESS aGlobal1! Creates a LOCAL named 
aGlobal1
        aGlobal2 = arg2 #because of the global statement, this really does
                        #access the expected global


        To get to stuff in an imported module, in a way that the module also 
sees it, requires 

import module

module.globallevelname ...


        Do not use

from module import globallevelname

as that just makes reference to the module's name, and uses the same 
name in the importing file. The first time you assign to that name, you 
change the reference -- you do not change what was inside the module 
itself.

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