Calling a generator multiple times

Bruce Eckel Bruce at EckelObjects.com
Sun Dec 9 03:09:32 CET 2001


On 12/9/01 at 12:14 AM Alex Martelli wrote:

>Bruce Eckel wrote:
>        ...
>> I believe that this is too restrictive a definition. My
experience
>> of generators (from C++/STL) is that a generator is simply a
>> callable entity that returns an object every time you call it;
this
>> call takes no arguments so it is "generating" objects rather
than
>
>...so a Python generator such as:
>
>def imageneratorhonest(sequence1, sequence2):
>    for item in sequence1: yield item
>    for item in sequence2: yield item
>
>isn't a generator...?  

Exactly! It's actually the factory that creates the generator! The
code makes my point:

from __future__ import generators

def gen():
  while 1:
    yield 'spam'
    
g = gen()
print g
for i in range(5):
  print g.next()

This produces:  
<generator object at 0x00792FE0>
spam
spam
spam
spam
spam

'g' is the generator object, and when you call next() (which takes
no arguments, as I asserted), you get objects popping out. It's a
generator in exactly the sense that I described (perhaps not so
clearly): you don't give it any arguments when you call it, so it's
creating using some internal algorithm. The factory that creates
the generator can take arguments for its initialization. This is
just like creating a generator class that has a constructor that
probably takes arguments, and then using an object of that class
with some kind of argument-less call to create the objects. It's
just slicker using yield.


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