Generators in Python (chapter 4)

# Section 4.2: Generators

# Generating the elements of an array
def elements(a):
    for i in range(len(a)):
        yield a[i]

print("elements [1,2,3]:");
for i in elements([1,2,3]): print(i)
print("elements [1,2]:");
g = elements([1,2])     # returns a generator
print(next(g))          # prints "1"
print(next(g))          # prints "2"
try:
    print(next(g))          # raises the StopIteration exception
except StopIteration:
    print("No more elements")

def primes():
    """Generator for prime numbers"""
    p = [2]; yield 2
    m = 3
    while True:
        i = 0
        while i < len(p) and p[i] * p[i] <= m:
            if m % p[i] == 0: break
            i += 1
        else:
            p.append(m); yield m
        m += 2

print("Some prime numbers:", end=" ")
g = primes()
for i in range(20): print(next(g), end=" ")
print()

def factor(n):
    """Print the prime number factorization of n"""
    pr = primes()
    while n > 1:
        p = next(pr)
        while n % p == 0: print(p); n = n // p

print("Factoring 924:")
factor(924)

def generator():
    n = 0
    while True:
        yield n; yield (-n); n += 1

print("Generating some integers:", end=" ")
g = generator()
for i in range(20): print(next(g), end=" ")
print()