Generators and Iterators

generators.py

# generators and iterators
import random

def my_gen(in_str="This is a sentence."):
    """A generator that returns on character in a string per iteration"""
    for char in in_str:
        yield char  # return one character and wait

def big_list():
    """Create a list of number from 0 to 100 million"""
    return list(range(100000000))

def list_gen():
    """A generator that gives you the same as above, but one at a time"""
    for i in range(100000000):
        yield i

# classic list comprehension
l_comp = [x for x in range(10)]

# generator comprehension. returns a generator
g_comp = (x for x in range(10))

class AlphaIter:
    """This class defines a new iterator which loops over the alphabet"""
    def __init__(self, count=10):
        self._max = count  # controls when the iterator runs out
        self._count = 0    # keep track of current iteration nunber
        self._pos = -1     # keep track of current alphabet position
        self._alpha = "abcdefghijklmnopqrstuvwxyz"

    def __iter__(self):
        """When something is trying to use this class as an iterator,
        return an instance of the class
        """
        return self

    def __next__(self):
        """This is what runs in every iteration. Controls what is returned"""
        if self._count >= self._max:
            raise StopIteration  # Stop iterating when we reach the max
        if self._pos >= 25:
            self._pos = -1       # Move back to "a"
        self._pos += 1           # increment our counters
        self._count += 1
        return self._alpha[self._pos]

class RandomChar(AlphaIter):
    """Similar to the class above, but returns a random letter"""
    def __init__(self, count=10):
        super().__init__(count=count)

    def __next__(self):
        if self._count >= self._max:
            raise StopIteration
        self._count += 1
        return random.choice(self._alpha)