a let b move forward first

Fibonancci.py

def sum_two_numbers(a, b):
    return a + b  # return result to the function caller


c = sum_two_numbers(3, 12)  # assign result of function execution to variable 'c'


def fib(n):
    """This is documentation string for function. It'll be available by fib.__doc__()
    Return a list containing the Fibonacci series up to n."""
    result = []
    a = 1
    b = 1

    # while a < n:
    #     result.append(b)
    #     tmp_var = a
    #     a = b + a
    #     b = tmp_var
    # return result

    #     or we could write: because what store in temp should be change first

    while a < n:
        result.append(a)
        tmp_var = b
        b = b + a
        a = tmp_var

    return result


print(fib(10))

# output [1, 1, 2, 3, 5, 8]