Python Programming

Advanced topic! You can skip this if you prefer.

If you do not need the values of a list pre-stored in memory, you can use generator expressions instead of list comprehension. Syntax-wise, you just replace the square brackets with parentheses.

>>> generator = (number*number for number in range(100000))
>>> next(generator)
0
>>> next(generator)
1
>>> next(generator)
4
>>> next(generator)
9

Generator expressions are useful if you expect a list to be large and you need to conserve memory space.

One example usage would be to pass the generator to a function that is expecting any iterable object as an input argument (list, range, enumerate, zip are all iterables). You conserve some memory space compared to passing a list. For example, you can pass a generator expression to the sum() function.

>>> sum(number*number for number in range(100000))

generator = (number*number for number in range(100000))
for number in generator:
    if number % 3 == 0:
        print(number)