Iterator Design Pattern
Videos
| Section | Video Links |
|---|---|
| Iterator Overview |    |
| Iterator Use Case | |
| Python iter() Function | |
Book
Overview
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Terminology
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Iterator UML Diagram
Source Code
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Output
python ./iterator/iterator_concept.py This method has been invoked This method has been invoked This method has been invoked This method has been invoked
Example Use Case
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Example UML Diagram
Output
python ./iterator/client.py 2, 4, 6, 8, 10, 1, 3, 5, 7, 9, 0, 2, 4, 6, 8, 10, 1, 3, 5, 7, 9, 0,
New Coding Concepts
Python iter()
Python Lists, Dictionaries, Sets and Tuples are already iterable, so if you want basic iteration for use in a for loop, then you only need to add your objects into one of those and it can be used right away.
NAMES = ['SEAN','COSMO','EMMY'] for name in NAMES: print(name, end=", ") #SEAN, COSMO, EMMY,
also, you can instantiate an iterable from the List, Dictionary, Tuple or Set by using the Python iter() method, or its own __iter__() dunder method, and then iterate over that using the __next__() method.
NAMES = ['SEAN','COSMO','EMMY'] ITERATOR = iter(NAMES) print(ITERATOR.__next__()) print(ITERATOR.__next__()) print(ITERATOR.__next__())
or
NAMES = ['SEAN','COSMO','EMMY'] ITERATOR = NAMES.__iter__() print(ITERATOR.__next__()) print(ITERATOR.__next__()) print(ITERATOR.__next__())
The Python iter() method also can accept a sentinel parameter.
The sentinel parameter is useful for dynamically created objects that are returned from an iterator and indicates where the last item is in the iterator by raising a StopIteration exception.
Usage : iter(object, sentinel)
When using the sentinel, the object passed as the first argument in the iter() method will need to be callable.
class Doubler(): count = 1 @classmethod def next(cls): cls.count *= 2 return cls.count __call__ = next ITERATOR = iter(Doubler(), 32) print(list(ITERATOR)) # Outputs [2, 4, 8, 16]
The __call__ = next line in the example above is setting the default method of the class to be next and that makes the class callable. See Dunder call Method for more information.
Also note that the list being printed at the end is automatically filled from the iterator. The list constructor utilizes the default callable method and the StopIteration exception automatically during its creation without needing to write this in the code.
Summary
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