Fibonacci numbers in Python.

The program

Press Run to see what it prints. Change anything you like, then run it again.

fib = [1, 1]
while len(fib) < 15:
    fib.append(fib[-1] + fib[-2])
print(fib)
ratios = [round(fib[i + 1] / fib[i], 4) for i in range(8, 13)]
print("Ratios:", ratios)

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610]
Ratios: [1.6176, 1.6182, 1.618, 1.6181, 1.618]

How it works

1. A list holds many values in order. fib[-1] is the last one and fib[-2] is the one before it.
2. append adds a value to the end. The loop runs until the list has 15 numbers.
3. The last two lines divide each number by the one before it. The answers get closer and closer to 1.618..., the golden ratio. A list comprehension builds a new list in one line.

Try this

• Make a list of 30 numbers.
• Print only the even Fibonacci numbers.
• Start with different numbers, such as [2, 1], and see what changes.

Stuck on an error? Read how to debug Python.