[Tutor] increment a counter inside generator

[David Knupp]

On Wed, 13 Mar 2013, Oscar Benjamin wrote:
> (it's not actually a generator by the way)

As Oscar points out, you're not working with a generator expression. The 
syntactical difference between a list comprehension and a generator 
expression is subtle. List comprehensions use square brackets, but 
generator expressions use parentheses.

>>> foo = [n for n in xrange(10)]
>>> foo
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> bar = (n for n in xrange(10))
>>> bar
<generator object at 0xb7eaadec>

FWIW, if you're working with very large lists, but don't need to create 
the full list in memory, then a generator expression is usually preferred. 
To get the number of items a generator would return, you can use sum() 
like this:

>>> gen = (n for n in xrange(some_really_huge_number))
>>> sum(1 for n in gen) # outputs some_really_huge_number

--dk.