On 14/03/2013 01:13, David Knupp wrote:
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.
There is little point in creating a generator from an xrange object.
Quoting from
http://docs.python.org/2/library/stdtypes.html#typesseq-xrange "The
xrange type is an immutable sequence which is commonly used for looping.
The advantage of the xrange type is that an xrange object will always
take the same amount of memory, no matter the size of the range it
represents. There are no consistent performance advantages."
--
Cheers.
Mark Lawrence
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