What is module initialization?

Bruno Desthuilliers bruno.42.desthuilliers at websiteburo.invalid
Tue Sep 2 16:04:34 CEST 2008

dudeja.rajat at gmail.com a écrit :
> Hi,
> I found on the net that there is something called module
> initialization.

The Python C api has a module init function for C-coded modules. There's 
no need for such a thing in pure Python modules since all the top-level 
code is executed when the module is loaded (as a main script or the 
first time the module is imported).

> Unfortunately, there is not much information for this.
> However, small the information I found module initialization can be of
> use to me in my project.
> I'm currently messing with a problem where I'm keeping my global
> variables ( or symbols) in a module and the other mdoules in the
> project acess these global variables.

remember that there's no such thing as a truely global namespace in 
Python. "global" really means "module level".

> However, there is one case when a module updates one such global
> variable

While this is technically legal, you should restrain yourself from doing 
such a thing, unless you *really* know what you're doing and why.

> but the variable is not getting updated in the module
> containing global symbols ( variables).

I suspect you didn't use a qualified name when importing. You have to do 
it this way :

# myglobals.py:
answer = 42

# question.py
import myglobals
myglobals.answer = "WTF ?"

> So, I thought of using this module initialization where I will
> intialize the module only once to update that variable. Ans in the
> rest of the program where ever this module is imported I shall be able
> to easily access the update value of the variable.
> Could some one provide me a sample code of module intialization?

All statements at the top-level of a module are executed when the module 
is loaded. That's all it takes wrt/ module initialization.

> And
> how can I ensure that module initialization is done only once?

Unless you're doing weird things with __import__ or the imp module, you 
shouldn't have to worry. import do two things : locate, load *and cache* 
the module *if* it isn't already in cache, and bind names into the 
importing namespace.

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