Comparing recursive and iterative fibonacci functions

fibonacci.py

# Calculate a number in a Fibonacci series,
# starting at fib(0) == 0 and fib(1) == 1.
# An iterative and a recursive implementation.
# Which one most clearly shows what the code does?

def iterative_fibonacci(x):
    a, b = 0, 1
    for n in range(x):
        a, b = b, a + b
    return a

def recursive_fibonacci(x):
    if x == 0:
        return 0
    elif x == 1:
        return 1
    else:
        return recursive_fibonacci(x - 1) + recursive_fibonacci(x - 2)

# The first lines of recursive_fibonacci could be replaced by
#
#    if x in (0, 1):
#        return x
#
# but IMO it makes the code less clear.
# fib(x)==x happens to be true for x in (0, 1) but it's normally not written
# like that when you define the Fibonacci series.

# Tests
for fib in (iterative_fibonacci, recursive_fibonacci):
    result = [fib(x) for x in range(8)]
    assert [0, 1, 1, 2, 3, 5, 8, 13] == result, 'result for ' + str(fib) + ': ' + str(result)