6.py

"""
https://stackoverflow.com/questions/2776829/difference-between-python-generators-vs-iterators
http://www.diveintopython3.net/iterators.html
https://docs.python.org/2/library/stdtypes.html#string-formatting
"""

list1 = ['a', 'b', 'c', 'd']

"""
Iterating through that list is easily done of course. But say you wanted to go through each item on the list and
then print only 'c' in that list?  And without using a loop? I'm not sure why you'd want to do it - but I guess it couldn't hurt to know :D

Note that the counter is preserved internally and it correctly moves to the next object. 'next' is the ONLY
method that the iterator has.
"""

iterator = iter(list1)
iterator.next()
iterator.next()
print(iterator.next())

"""
Writing your own custom iterators is so you can iterate through them and perform whatever operations you want to
on them. Its a good idea to read the stack overflow thread that I refer to at the top - to understand why one
would need to even use custom iterators.

To understand custom iterators though, we first need to understand classes. If you have a simple program, then
you can probably write clean code - just using modules and importing them. Classes are apparently the OOP way
of doing things - I am unclear yet, as to what advantages they offer. So please help :)

All the same, here is a code snippet that shows how to define classes AND custom iterators.
"""

class Test:
    """
    This is how a class is defined along with its methods. The first 3 methods are compulsory
    if you want to create your own iterator. All the fancy filtering logic should go into the next() method.
    """
    def __init__(self, number):
        self.number = number

    def __iter__(self):
        return self

    def next(self):
        fib = self.number
        fib += 2
        self.number = fib
        if fib >= 15:
            raise StopIteration

        return fib

    """
    Since this is a class, you can, in addition to the 3 "iterator" methods, also define additional methods.
    These methods can be invoked by an object as usual.
    """
    def additionalmethod(self):
        print("You can define additional methods here and call that normally")

for i in Test(1):
    """
        This causes the custom next() method of the class to get invoked and jumps 2 steps at a time, instead of 1 by default, had you just
        called next().
        Use format strings instead of concatenating and using str() or repr() to print things.
    """
    print("Value of i is %s" %i)
    print("test", 123)

    print "For python 3 you can use a separator here. Look at the comments for the syntax"
    # print("test", 123, sep=':')

t1 = Test(0)
t1.additionalmethod()