pyFibonacci (Without Recursion)

# Generate Fibonacci Series

# Mike Kerry - 25-Jan-2021 - acclivity2@gmail.com

# Very often, the solution to generating the Fibonacci series is coded to use a recursive function
# I don't see the point as it is trivial to use a simple loop

while True:     # keep looping until an acceptable value is entered for the number of fibonacci elements
    strin = input("How many numbers in the Fibonacci series do you want? " ).strip()

    # isdecimal() checks that the input string consists of 0 to 9 only
    if strin.isdecimal() and int(strin) > 2:
        break               # here we exit the loop if an acceptable value has been entered

limit = int(strin)          # convert the valid input to an integer

fiblist = [1, 1]            # We start with knowledge of the first 2 numbers in the Fibonacci sequence

# We want to loop (limit - 2) times, but we have no need to know what loop number we are on, hence _ is used as loop control
for _ in range(limit - 2):
    # use list splicing to access the last two integers in the series so far, and add them together using sum()
    # fiblist[-2:] references the last 2 numbers in fiblist.
    # The first time, this will be 1, 1 which are summed and appended to the list. So the list then becomes 1, 1, 2
    # On the second time, the last 2 items in fiblist are 1, 2. These are summed and appended, resulting in 1, 1, 2, 3
    # On cycle three, 2 + 3 = 5 resulting in 1, 1, 2, 3, 5 in fiblist
    # and so on
    fiblist.append(sum(fiblist[-2:]))

print(*fiblist)

# Results:

# How many numbers in the Fibonacci series do you want? 18
# 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584