Programa de Python para números de Fibonacci

Los números de Fibonacci son los números en la siguiente secuencia de enteros.
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ……..
En términos matemáticos, la secuencia Fn de los números de Fibonacci está definida por la relación de recurrencia 

    Fn = Fn-1 + Fn-2

con valores semilla  

# Function for nth Fibonacci number
def Fibonacci(n):
   
    # Check if input is 0 then it will
    # print incorrect input
    if n < 0:
        print("Incorrect input")
 
    # Check if n is 0
    # then it will return 0
    elif n == 0:
        return 0
 
    # Check if n is 1,2
    # it will return 1
    elif n == 1 or n == 2:
        return 1
 
    else:
        return Fibonacci(n-1) + Fibonacci(n-2)
 
# Driver Program
print(Fibonacci(9))
 
# This code is contributed by Saket Modi
# then corrected and improved by Himanshu Kanojiya

# Function for nth fibonacci
# number - Dynamic Programming
# Taking 1st two fibonacci numbers as 0 and 1
FibArray = [0, 1]
 
def fibonacci(n):
   
    # Check is n is less
    # than 0
    if n < 0:
        print("Incorrect input")
         
    # Check is n is less
    # than len(FibArray)
    elif n < len(FibArray):
        return FibArray[n]
    else:       
        FibArray.append(fibonacci(n - 1) + fibonacci(n - 2))
        return FibArray[n]
 
# Driver Program
print(fibonacci(9))
 
# This code is contributed by Saket Modi

# Function for nth fibonacci
# number - Space Optimisation
# Taking 1st two fibonacci numbers as 0 and 1
 
def fibonacci(n):
    a = 0
    b = 1
     
    # Check is n is less
    # than 0
    if n < 0:
        print("Incorrect input")
         
    # Check is n is equal
    # to 0
    elif n == 0:
        return 0
       
    # Check if n is equal to 1
    elif n == 1:
        return b
    else:
        for i in range(1, n):
            c = a + b
            a = b
            b = c
        return b
 
# Driver Program
print(fibonacci(9))
 
# This code is contributed by Saket Modi
# Then corrected and improved by Himanshu Kanojiya