Importing again and again

[Laszlo Nagy]

abcd írta:
> If I have code which imports a module over and over again...say each
> time a function is called, does that cause Python to actually re-import
> it...or will it skip it once the module has been imported??
>
> for example:
>
> def foo():
>     import bar
>     bar.printStuff()
>
> foo()
> foo()
> foo()
> foo()
>
> ...will that re-import bar 4 times...or just import it once? 
Just once. Try this:

bar.py:

print "I have been imported"

def printStuff():
    print "printStuff was called"

foo.py:

def foo():
    import bar
    bar.printStuff()

foo()
foo()
foo()


The result is:

I have been imported
printStuff was called
printStuff was called
printStuff was called


If you really need to reimport the module, you can do this:

foo.py:

import bar

def foo():
    global bar
    bar = reload(bar)
    bar.printStuff()

foo()
foo()
foo()


The result is:

I have been imported
I have been imported
printStuff was called
I have been imported
printStuff was called
I have been imported
printStuff was called


> Is this a big performance hit?
>   
It depends on the size of your 'bar.py' module, and also it depends on 
how often you need to change/reload while your program is running.

Best,

   Laszlo