[Tutor] Importing question

[Kent Johnson]

Dick Moores wrote:
> At http://wiki.python.org/moin/SimplePrograms I found this code:
> 
> ============================================
> import itertools
> 
> def iter_primes():
>      # an iterator of all numbers between 2 and +infinity
>      numbers = itertools.count(2)
> 
>      # generate primes forever
>      while True:
>          # get the first number from the iterator (always a prime)
>          prime = numbers.next()
>          yield prime
> 
>          # this code iteratively builds up a chain of
>          # filters...slightly tricky, but ponder it a bit
>          numbers = itertools.ifilter(prime.__rmod__, numbers)
> 
> for p in iter_primes():
>     if p > 1000:
>         break
>     print p
> ====================================================
> 
> It works for me in Win XP, Python 2.5.
> 
> However, in trying to dig into the code to understand it, I'm not able 
> to find itertools.py, even though itertools is found in the docs at < 
> http://www.python.org/doc/2.4/lib/module-itertools.html>.
> A search of my Python25 directory doesn't turn up an itertools.py.
> 
> So my question is, how does the first line of the code work? /Where /is 
> itertools?

You can find out where any module is located using its __file__ 
attribute. This works for modules written in C, too. On my (Mac OSX) 
computer:
In [2]: itertools.__file__
Out[2]: 
'/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/lib-dynload/itertools.so'

Kent