"generator expressions" in python…

[Humble]

If you havent gone through previous post on list comprehension please do so .. As noted there, list comprehensions act on sequence and produce a list output which is fast and efficient.. But if this list is just an intermediate step in your python expression, use generator expressions.

Why ? It saves memory!!!

Instead of storing the resulted list, generators return only one item of the list at a time.

If you know list comprehensions , you can use the same syntax for generator expressions as well with a small difference that, list comprehensions use [] when generator expressions use ()

list comprehension example:

>>> [x for x in range(1,10) ]
[1, 2, 3, 4, 5, 6, 7, 8, 9]




generator expression example

>>> (x for x in range(1,10) )
<generator object <genexpr> at 0x7fa5d0252eb0>

>>> y= (x for x in range(1,10) )

generator object have "next" method as shown below:

>>> y.next
<method-wrapper 'next' of generator object at 0x7fa5d01facd0>




so, we can even make use of "next()" to get next item:

>>> y.next()
1
>>> y.next()
2
>>> y.next()
3
>>> y.next()
4
>>> y.next()
5
>>> y.next()
6
>>> y.next()
7
>>> y.next()
8
>>> y.next()
9




If there are no more elements, it return "StopIteration" exception :

>>> y.next()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

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