![Example generator
In [65]: def example_generator(): # Is a function
...: yield 1 # Has **yield**
...: yield 2 # Can have more than 1 yield
...:
In [66]: for each in example_generator(): # Generator instances are mostly used
with for
...: print each
...:](https://image.slidesharecdn.com/generators-171118080734/85/Python-Generators-4-320.jpg)
Python Generators
- 1. Generators
- 2. Why generators? ● Writing memory optimized code. ● Understanding how Python web framework works. Eg: Django, Flask ● Writing simpler, abstracted code. We will see an example at the end.
- 3. What is a generator? ● Function ● Function having yield keyword ● Lazy evaluation
- 4. Example generator In [65]: def example_generator(): # Is a function ...: yield 1 # Has **yield** ...: yield 2 # Can have more than 1 yield ...: In [66]: for each in example_generator(): # Generator instances are mostly used with for ...: print each ...:
- 5. Without generator ● Memory consuming code ● Custom implementation of range, custom_range() ● 4 million numbers would take ~ 100 MB
- 6. With generator ● Memory efficient code ● Custom implementation of xrange, custom_xrange(). ● 4 million numbers would take 24 bytes
- 7. Generator control flow ● Execution suspends on encountering yield. ● Execution resumes with next iteration. ● Execution stops on encountering return.
- 8. Real world usage ● xrange() ● os.walk() ● File operations: Reading, searching etc. ● itertools.permutations()
- 9. Generators and Iterators ● Every generator is an iterator but not vice versa. ● Generator instances are iterables. They can be used with iter()
- 10. Recap ● Iterable must implement __iter__(). No need to implement next(). ● Iterator must implement next(). No need to implement __iter__() ● iter() must be used with Iterable. ● next() must be used with iterator.
- 11. How for loop works ● **for** works with an iterable which must have an underlying iterator. ● iter(iterable) is called which returns a iterator. ● next() of iterator is repeatedly called until StopIteration is raised from next().
- 12. Why generator over iterators ● Generator functions are convenient shortcuts to build iterators. ● Generators remove boilerplate. ● Compare class xrange_iterator() with generator custom_xrange().