{"id":638,"date":"2020-10-18T08:11:58","date_gmt":"2020-10-18T08:11:58","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=638"},"modified":"2025-03-27T03:05:49","modified_gmt":"2025-03-27T03:05:49","slug":"python-issubset","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-issubset\/","title":{"rendered":"Python issubset"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about how to use the Python issubset()<\/code> method to check if a set<\/a> is a subset of another set.<\/p>\n\n\n\n

Introduction to the Python issubset() method #<\/a><\/h2>\n\n\n\n

Suppose that you have two sets A and B. Set A is a subset of set B if all elements of A are also elements of B. Then, set B is a superset of set A.<\/p>\n\n\n\n

The following Venn diagram illustrates that set A is a subset of the set B:<\/p>\n\n\n

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\"Python<\/figure>\n<\/div>\n\n\n

Set A and set B can be equal. If set A and set B are not<\/strong> equal, A is a proper<\/strong> subset of B.<\/p>\n\n\n\n

In Python, you can use the Set issubset()<\/code> method to check if a set is a subset of another:<\/p>\n\n\n

set_a<\/span>.issubset<\/span>(set_b<\/span>)<\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\n
If the set_a<\/code> is a subset of the set_b<\/code>, the issubset()<\/code> method returns True<\/code>. Otherwise, it returns False<\/code>.<\/p>\n\n\n\n
The following example uses the issubset()<\/code> method to check if the set_a<\/code> is a subset of the set_b<\/code>:<\/p>\n\n\n
numbers = {1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>}\nscores = {1<\/span>, 2<\/span>, 3<\/span>}\n\nprint<\/span>(scores.issubset(numbers))<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
By definition, a set is also a subset of itself. The following example returns True<\/code>:<\/p>\n\n\n
numbers = {1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>}\n\nprint<\/span>(numbers.issubset(numbers))<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The following example returns False<\/code> because some elements in the numbers<\/code> set aren’t in the scores<\/code> set. In other words, the numbers<\/code> set is not a subset of the scores<\/code> set:<\/p>\n\n\n
numbers = {1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>}\nscores = {1<\/span>, 2<\/span>, 3<\/span>}\n\nprint<\/span>(numbers.issubset(scores))<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
False<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Using subset operators #<\/a><\/h2>\n\n\n\n
Besides using the issubset()<\/code> method, you can use the subset operator (<=<\/code>) to check if a set is a subset of another set:<\/p>\n\n\n
set_a <= set_b<\/code><\/span><\/pre>\n\n\n
The subset operator (<=<\/code>) returns True<\/code> if set_a<\/code> is a subset of the set_b<\/code>. Otherwise, it returns False<\/code>. For example:<\/p>\n\n\n
numbers = {1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>}\nscores = {1<\/span>, 2<\/span>, 3<\/span>}\n\nresult = scores <= numbers\nprint<\/span>(result)  # True<\/span>\n\nresult = numbers <= numbers\nprint<\/span>(result)  # True<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The proper subset operator (<<\/code>) check if the set_a<\/code> is a proper subset of the set_b<\/code>:<\/p>\n\n\n
set_a < set_b<\/code><\/span><\/pre>\n\n\n
For example:<\/p>\n\n\n
numbers = {1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>}\nscores = {1<\/span>, 2<\/span>, 3<\/span>}\n\nresult = scores < numbers\nprint<\/span>(result)  # True<\/span>\n\nresult = numbers < numbers\nprint<\/span>(result)  # False<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the set numbers<\/code> is not a proper subset of itself, therefore, the <<\/code> operator returns False<\/code>.<\/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