[Tutor] Importing global variables and classes from other modules

[Danny Yoo]

On Sun, 21 Dec 2003, Venkatesh Babu wrote:

> I have a main module which has few functions and in one of the
> functions, I have given an import statement so that I can get the
> functions and global variables present in other module into my main
> module's name space.

Hi Venkatesh,

Other folks have already pointed out why the above isn't working.  But
just as a reality check: are you sure you want to do this?


It's usually a very bad idea to do a 'from foo import *' --- it ties
together your module extremely closely to the imported module, and it
becomes a lot more difficult to see where a certain variable came from.

Simple example: if I see the code,

###
def f():
    print 'hello'

from some_module import *

f()
###

then I have no idea if the last function call, 'f()', refers to the f
that's just been defined at the top.  Why would I feel worried?  Because
any name in 'some_module' may have clobbered things in my own namespace,
and if 'some_module' itself defines an 'f', that'll override my 'f'.


The official Python Tutorial mentions 'from foo import *' is a statement
to avoid writing in real code:

http://python.org/doc/current/tut/node8.html#SECTION008410000000000000000


If you must make a module with global variables, it might be best to just
do the simple import:

###
import global_module
###

and refer to values in that module by explicitely refering to
global_module:

###
print global_module.some_variable_name
###



> But my problem is that the functions and other global variables present
> sub are not getting imported to my main module. Can any body suggest me
> what is the right method to do, the condition being that the import
> should happen only if I call f1.

Wait, wait.  Doing a conditional import might be a very bad idea from a
debugging standpoint.

Can you show us why you want to import this way?  That context might help
us to suggest better alternatives, if there are any.


Good luck to you!