What is module initialization?

[dudeja.rajat]

Hi,

I found on the net that there is something called module
initialization. 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.

However, there is one case when a module updates one such global
variable but the variable is not getting updated in the module
containing global symbols ( variables). This happen only at the start
of the program and at rest of the places in the program that global
variable is not accessed.

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

Thanks and regards,
Rajat

 

[Marc 'BlackJack' Rintsch]

I found on the net that there is something called module initialization.
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.

"Module initialization" is what happens when you import a module the
first time. In pure Python modules the module level code is executed and
in extension modules a special initializing function may be called.

However, there is one case when a module updates one such global
variable but the variable is not getting updated in the module
containing global symbols ( variables).

Sounds unlikely if you *really* update the attribute of the module and
not just rebind a local name that was bound to the object in the "global"
module before. Example:

from spam import egg

egg = 42 # This does *not* change `spam.egg` but just the local binding!

Could some one provide me a sample code of module intialization? And how
can I ensure that module initialization is done only once?

Module initialization is only done once, there's nothing to ensure.

Ciao,
Marc 'BlackJack' Rintsch

 

[Bruno Desthuilliers]

(e-mail address removed) 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.

 

[dudeja.rajat]

While this is technically legal, you should restrain yourself from doing

such a thing, unless you *really* know what you're doing and why.


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 ?"

But if I do :-
#question.py
from myglobals import *
myglobals.answer = "WTF ?"

will this work?

 

[Fredrik Lundh]

But if I do :-
#question.py
from myglobals import *
myglobals.answer = "WTF ?"

will this work?

with the above definition of myglobals, no. "from myglobals import"
doesn't add the module object to the importing module's namespace.

have you read:

http://effbot.org/zone/import-confusion.htm

?

</F>

 

[dudeja.rajat]

with the above definition of myglobals, no. "from myglobals import" doesn't
add the module object to the importing module's namespace.

have you read:

http://effbot.org/zone/import-confusion.htm

?

</F>

Thanks for your help guys that I got my problem resolved.



Regards,
Rajat