What does the "yield" keyword do in Python?

Abstraction: Python yield keyword creates generator objects lazily

Key points:

• yield turns a function into a generator — calling the function returns a generator object without executing the body
• Generators are iterators you can only iterate over once; values are computed on the fly, not stored in memory
• Execution resumes from where it left off each time for calls next() on the generator
• Generator exhaustion occurs when the function returns without hitting yield (loop ends or condition fails)
• itertools module provides advanced generator utilities: permutations, chain, tee, izip, etc.
• Duck typing means Python's extend() and similar methods accept any iterable, including generators

Connections: Python · Generators · Lazy Evaluation · Iterators

Source: http://stackoverflow.com/questions/231767/the-python-yield-keyword-explained