the yield keyword in python

Q. Why use lazy iterators?
A. To solve memory issue. use the yield keyword instead or return inside functions
E. Reading a list of large files (~GB) into python list can cause memory issue, so return a lazy iterator, or generator in python, which will lazy load these things when they are needed.

Q. What does generator consists of?
A. some metadata like state of the function, variable binding, instruction pointer, internal stack etc.

For detailed instruction, this link has a good example.