Exercise: genPrimes

Write a generator,genPrimes, that returns the sequence of prime numbers on successive calls to its next()method: 2, 3, 5, 7, 11, ...

 Note that our solution makes use of the for/else clause, which 
# you can read more about here:
# http://docs.python.org/release/1.5/tut/node23.html 

def genPrimes():
    primes = []   # primes generated so far
    last = 1      # last number tried
    while True:
        last += 1
        for p in primes:
            if last % p == 0:
                break
        else:
            primes.append(last)
            yield last

Exercise 2

• Every procedure that has ayieldstatement is a generator.

True

https://docs.python.org/release/2.3.5/ref/yield.html

Using a yield statement in a function definition is sufficient to cause that definition to create a generator function instead of a normal function.

• If we were to use a generator to iterate over a million numbers, how many numbers do we need to store in memory at once?

We need to store 2 numbers - one for the current value, and one for the max value.