Fibonacci series in python.

fibonacci.py

# Version 1
def fib(n):
    if n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n-1) + fib(n-2)
        
# Version 2
def fib(n):
    if n == 0 or n == 1:
        return n
    else:
        return fib(n-1) + fib(n-2)
        
# Version 3
def fib(n):
    if n in (0,1):
        return n
    else:
        return fib(n-1) + fib(n-2)
        
# Version 4
def fib(n):
    if n in (0,1):
        return n
    return fib(n-1) + fib(n-2)
    
# Version 5
def fib(n):
    if n in (0, 1): return n
    return fib(n-1) + fib(n-2)
    
# Version 6
def fib(n):
    return (n in (0,1) and [n] or [fib(n-1) + fib(n-2)])[0]

# Version 7
fib = lambda n: (n in (0,1) and [n] or [fib(n-1) + fib(n-2)])[0]