Iterators, Generators and List Comprehensions

Python Tutorials - Herong's Tutorial Examples

∟Iterators, Generators and List Comprehensions

This chapter provides introductions and tutorial examples about iterators, generators and list comprehensions. Topics include introduction on iterable objects, iterators, generators, and list comprehensions; list of built-in iterable data types; using 'yield' statements and generator functions; using generator expressions and list comprehensions.

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What Is Iterator Object

What Is Iterable Object

Iterable Objects of Built-in Data Types

What Is Generator Iterator

What Is Generator Expression

What Is Filtered Generator Expression

What Is Double-Generator Expression

What Is List Comprehension

What Is Filtered List Comprehension

What Is Double-List Comprehension

Generator Expression vs. List Comprehension

Takeaways:

An iterator object supports a required instance method, iterator.__next__(), to return the next item.
An iterable object supports a required instance method, iterable.__iter__(), to return an iterator object.
isinstance(object, collections.abc.Iterable) can be used to test if a given object is iterable or not.
For built-in iterable objects, their iterators are also iterable.
A generator iterator is an iterator object created by a generator function or a generator expression.
A generator function is a special function that contains one or more "yield" statements.
A "yield" statement transforms the enclosing function into a generator function. It suspends and resumes execution to support next(generator) calls.
A generator expression transforms an expression into a generator with a "for" clause enclosed in parentheses.
A filtered generator expression is a generator expression with an "if" sub-clause to filter out items with a given condition.
A double-generator expression is a generator expression that contains a double "for" clause to iterate two iterables sequentially.
A list comprehension creates a list object using a "for" clause enclosed in square brackets.
A filtered list comprehension is a list comprehension with an "if" sub-clause to filter out items with a given condition.
A double-list comprehension is a list comprehension that contains a double "for" clause to iterate two iterables sequentially.
Generator expressions and list comprehensions have almost identical syntaxes: (EXPRESSION for ...) vs. [EXPRESSION for ...]
Generator expressions return "generator" objects.
List comprehensions return "list" objects.
Generator expressions use "late-binding" to support next(generator) calls to reduce memory usage.