14-Iterators&Generators

Iterator

• An object that can be iterated upon, something we can run a for loop over
• Behind the scenes, for loop calls the next() method and it returns the next item in the loop
  • One item at a time
  • Until it raises a StopIteration error, i.e, at last item

Iterable

• An object that returns an Iterator when iter() is called
• When we loop over something (str, list, etc.), for loop calls the iter() function on it behind the scenes and makes it into an iterator

Generators

• Subset of iterators
• Every generator is an iterator but not vice-versa
• Easy way to create iterators
  • One way is to use generator functions using yield keyword
  • Another way to create generators is w generator expressions

Generator Functions

• Just like a normal function but uses yield instead of return
• Can yield multiple times unlike normal function that return only once
• Returns a generator object when invoked
• It only stores one thing at a time until it's changed any time we call the next method on it

Generator Expressions

• Easier way to create generators
• Look like list comprehensions for lists
• We use () instead of []
• It's more like Tuple Comprehension in syntax

g = (num for num in range(1, 10))
# g here is generator object created from generator expression