The classic Fibonacci generator example

First, a plain function to generate the Nth number in the Fibonacci series:



In [1]:

    
def fibonacci(n):
    a, b = 0, 1
    while n:
        a, b = b, a + b
        n -= 1
    return a



In [2]:

    
for n in range(10):
    print(fibonacci(n))



In [3]:

    
[fibonacci(n) for n in range(10)]









    Out[3]:





[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

The generator

Now, a generator function



In [4]:

    
def gen_fibo(n):
    a, b = 0, 1
    while n:
        yield a
        a, b = b, a + b
        n -= 1



In [13]:

    
g10 = gen_fibo(10)
g10









    Out[13]:





<generator object gen_fibo at 0x7fb294710410>



In [14]:

    
f10 = list(g10)
f10









    Out[14]:





[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]



In [15]:

    
for n in gen_fibo(n):
    print(n)



In [7]:

    
f10 = list(gen_fibo(10))
ratios = [a/b for a, b in zip(f10[2:], f10[1:-1])]
ratios









    Out[7]:





[1.0,
 2.0,
 1.5,
 1.6666666666666667,
 1.6,
 1.625,
 1.6153846153846154,
 1.619047619047619]



In [8]:

    
φ = (1 + 5**0.5) / 2
φ









    Out[8]:





1.618033988749895



In [10]:

    
%matplotlib inline

import matplotlib.pyplot as plt

plt.figure()
plt.plot(ratios)
plt.axhline(φ, color='r')









    Out[10]:





<matplotlib.lines.Line2D at 0x7fb297115438>