Question

In python: I am trying to construct a list using enumerate and takewhile from a Fibonaci generator. So far the code I have is the following:

def fibonacci():
(a, b) = (0, 1)
while True:
yield a
(a, b) = (b, a + b)

def createlist(n, fib):
return [elem for (i, elem) in enumerate(takewhile(lambda x: x < n, fib)) if i < n]

I only get half the list when I do:

print(createlist(n, fibonacci()))

Output: [0, 1, 1, 2, 3, 5, 8]

Expected Output: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34], when n = 10.

Am I missing something in the predicate of takewhile? Could I use a counter inside takewhile? I was specifically asked to use takewhile and enumerate.

Answer 1

I have used Counter inside fibonacci() and in takewhile() i have compared Counter with n value

from itertools import takewhile
def fibonacci():
    global count
    count=0
    (a, b) = (0, 1)
    while True:
        count+=1
        yield (a,count)
        (a, b) = (b, a + b)
def createlist(n, fib):
    return [elem[0] for (i, elem) in enumerate(takewhile(lambda x: x[1]<=n, fib))]
print(createlist(10,fibonacci()))

Output