9.4.2 List from iterators

Iterators provide us with an elegant solution to problems discussed previously:

def result_iterator():
    for k in itertools.count(): # infinite iterator
        # call various functions here
        # that t lists compute "result"
        ...
        yield result

With iterators, we separate the task of generating the computed values without bothering about the stopping condition or about the storage.

• If the user of that code wants to store the  first values, it is easily done using the list constructor:

L = list(itertools.islice(result_iterator(), n)) # no append needed!

• If the user wants the sum of the first n generated values, this construction is recommended:

# make sure that you do not use numpy.sum here
s = sum(itertools.islice(result_iterator(), n))

• If the user wants to generate all elements until a certain condition is fulfilled, the function itertools.takewhile comes in handy:

L=list(itertools...