{"id":358,"date":"2020-10-07T09:24:00","date_gmt":"2020-10-07T09:24:00","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=358"},"modified":"2025-03-26T13:56:23","modified_gmt":"2025-03-26T13:56:23","slug":"python-iterables","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-iterables\/","title":{"rendered":"Python Iterables"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about the Python iterables and iterators.<\/p>\n\n\n\n

Introduction to Python iterables #<\/a><\/h2>\n\n\n\n

In Python, an iterable is an object that includes zero, one, or many elements. An iterable has the ability to return its elements one at a time.<\/p>\n\n\n\n

Because of this feature, you can use a for<\/code> loop <\/a>to iterate over an iterable.<\/p>\n\n\n\n

In fact, the range()<\/code> function is an iterable because you can iterate over its result:<\/p>\n\n\n

for<\/span> index in<\/span> range(3<\/span>):\n    print(index)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
0<\/span>\n1<\/span>\n2<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
str = 'Iterables'<\/span>\nfor<\/span> ch in<\/span> str:\n    print(ch)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
I\nt\ne\nr\na\nb\nl\ne\ns<\/code><\/span><\/pre>\n\n\n
Lists<\/a> and tuples<\/a> are also iterables because you can loop over them. For example:<\/p>\n\n\n
ranks = ['high'<\/span>, 'medium'<\/span>, 'low'<\/span>]\n\nfor<\/span> rank in<\/span> ranks:\n    print(rank)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The rule of thumb is that if you know if can loop over something, it’s an iterable.<\/p>\n\n\n\n
What is an iterator #<\/a><\/h2>\n\n\n\n
An iterable can be iterated over. And an iterator is the agent that performs the iteration.<\/p>\n\n\n\n
To get an iterator from an iterable, you use the iter()<\/code> function. For example:<\/p>\n\n\n
colors = ['red'<\/span>, 'green'<\/span>, 'blue'<\/span>]\ncolors_iter = iter(colors)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Once you have the iterator, you can get the next element from the iterable using the next()<\/code> function:<\/p>\n\n\n
colors = ['red'<\/span>, 'green'<\/span>, 'blue'<\/span>]\ncolors_iter = iter(colors)\n\ncolor = next(colors_iter)\nprint(color)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
red<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Every time, you call the next()<\/code> function, it returns the next element in the iterable. For example:<\/p>\n\n\n
colors = ['red'<\/span>, 'green'<\/span>, 'blue'<\/span>]\ncolors_iter = iter(colors)\n\ncolor = next(colors_iter)\nprint(color)\n\ncolor = next(colors_iter)\nprint(color)\n\ncolor = next(colors_iter)\nprint(color)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
red\ngreen\nblue<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
If there isn’t any more element and you call the next()<\/code> function, you’ll get an exception.<\/p>\n\n\n
colors = ['red'<\/span>, 'green'<\/span>, 'blue'<\/span>]\ncolors_iter = iter(colors)\n\ncolor = next(colors_iter)\nprint(color)\n\ncolor = next(colors_iter)\nprint(color)\n\ncolor = next(colors_iter)\nprint(color)\n\n# cause an excpetion<\/span>\ncolor = next(colors_iter)\nprint(color)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
This example first shows three elements of the colors list and then issues an exception:<\/p>\n\n\n
red\ngreen\nblue\nTraceback (most recent call last):\n  File \"iterable.py\"<\/span>, line 15<\/span>, in<\/span> <module>\n    color = next(colors_iter)\nStopIteration<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The iterator is stateful, meaning that once you consume an element from the iterator, it’s gone.<\/p>\n\n\n\n
In other words, once you complete looping over an iterator, the iterator becomes empty.  If you iterate over it again, it’ll return nothing.<\/p>\n\n\n\n
Since you can iterate over an iterator, the iterator is also an iterable object. This is quite confusing. For example:<\/p>\n\n\n
colors = ['red'<\/span>, 'green'<\/span>, 'blue'<\/span>]\niterator = iter(colors)\n\nfor<\/span> color in<\/span> iterator:\n    print(color)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
red\ngreen\nblue<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
If you call the iter()<\/code> function and pass an iterator to it, it’ll return the same iterator back.<\/p>\n\n\n\n
Later, you’ll learn how to create iterables.<\/p>\n\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Also, a string<\/a> is an iterable because you can use a for loop<\/a> to iterate over it:<\/p>\n\n\n
Try it<\/a><\/p>\n\n\n\n