{"id":628,"date":"2020-10-18T04:55:57","date_gmt":"2020-10-18T04:55:57","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=628"},"modified":"2025-03-27T03:03:31","modified_gmt":"2025-03-27T03:03:31","slug":"python-set-comprehension","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-set-comprehension\/","title":{"rendered":"Python Set Comprehension"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn how to use Python set comprehension to create a new set based on an existing one.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='introduction-to-python-set-comprehension'>Introduction to Python Set comprehension <a href=\"#introduction-to-python-set-comprehension\" class=\"anchor\" id=\"introduction-to-python-set-comprehension\" title=\"Anchor for Introduction to Python Set comprehension\">#<\/a><\/h2>\n\n\n\n<p>Suppose that you have the following <a href=\"https:\/\/www.pythontutorial.net\/python-basics\/python-set\/\">set<\/a> that consists of three tags:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">tags = {<span class=\"hljs-string\">'Django'<\/span>, <span class=\"hljs-string\">'Pandas'<\/span>, <span class=\"hljs-string\">'Numpy'<\/span>}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To convert the tags in the set to another set of tags in lowercase, you may use the following <a href=\"https:\/\/www.pythontutorial.net\/python-basics\/python-for-range\/\"><code>for<\/code> <\/a>loop:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">tags = {<span class=\"hljs-string\">'Django'<\/span>, <span class=\"hljs-string\">'Pandas'<\/span>, <span class=\"hljs-string\">'Numpy'<\/span>}\n\nlowercase_tags = set()\n<span class=\"hljs-keyword\">for<\/span> tag <span class=\"hljs-keyword\">in<\/span> tags:\n    lowercase_tags.add(tag.lower())\n\nprint(lowercase_tags)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pythontutorial.net\/playground\/?q=dGFncyA9IHsnRGphbmdvJywgJ1BhbmRhcycsICdOdW1weSd9Cgpsb3dlcmNhc2VfdGFncyA9IHNldCgpCmZvciB0YWcgaW4gdGFnczoKICAgIGxvd2VyY2FzZV90YWdzLmFkZCh0YWcubG93ZXIoKSkKCnByaW50KGxvd2VyY2FzZV90YWdzKQ%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">{<span class=\"hljs-string\">'django'<\/span>, <span class=\"hljs-string\">'numpy'<\/span>, <span class=\"hljs-string\">'pandas'<\/span>}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>How it works:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, iterate over each element of the <code>tags<\/code> set.<\/li>\n\n\n\n<li>Second, convert each tag to lowercase and add it the new set (<code>lowercase_tags<\/code>)<\/li>\n<\/ul>\n\n\n\n<p>Or you can use the built-in <code>map()<\/code> function with a lambda expression:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">tags = {<span class=\"hljs-string\">'Django'<\/span>, <span class=\"hljs-string\">'Pandas'<\/span>, <span class=\"hljs-string\">'Numpy'<\/span>}\nlowercase_tags = set(map(<span class=\"hljs-keyword\">lambda<\/span> tag: tag.lower(), tags))\n\nprint(lowercase_tags)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>map()<\/code> function returns a map object so you need to use the <code>set()<\/code> function to convert it to a set.<\/p>\n\n\n\n<p>To make the code more concise, Python provides you with the set comprehension syntax as follows:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">{expression <span class=\"hljs-keyword\">for<\/span> element <span class=\"hljs-keyword\">in<\/span> set <span class=\"hljs-keyword\">if<\/span> condition}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The set comprehension allows you to create a new set based on an existing set.<\/p>\n\n\n\n<p>A set comprehension carries the following steps:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, iterate over the elements of a set.<\/li>\n\n\n\n<li>Second, apply an <code>expression<\/code> to each element<\/li>\n\n\n\n<li>Third, create a new set of elements resulting from the expression.<\/li>\n<\/ul>\n\n\n\n<p>In addition, the set comprehension allows you to select which element to apply the expression via a <code>condition<\/code> in the <code>if<\/code> clause.<\/p>\n\n\n\n<p class=\"note\">Note that the set comprehension returns a new set, it doesn&#8217;t modify the original set.<\/p>\n\n\n\n<p>Back to the previous example, you can convert all the tags in the <code>tags<\/code> set by using the following set comprehension:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">tags = {<span class=\"hljs-string\">'Django'<\/span>, <span class=\"hljs-string\">'Pandas'<\/span>, <span class=\"hljs-string\">'Numpy'<\/span>}\nlowercase_tags = {tag.lower() <span class=\"hljs-keyword\">for<\/span> tag <span class=\"hljs-keyword\">in<\/span> tags}\n\nprint(lowercase_tags)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pythontutorial.net\/playground\/?q=dGFncyA9IHsnRGphbmdvJywgJ1BhbmRhcycsICdOdW1weSd9Cmxvd2VyY2FzZV90YWdzID0ge3RhZy5sb3dlcigpIGZvciB0YWcgaW4gdGFnc30KCnByaW50KGxvd2VyY2FzZV90YWdzKQ%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">{<span class=\"hljs-string\">'numpy'<\/span>, <span class=\"hljs-string\">'pandas'<\/span>, <span class=\"hljs-string\">'django'<\/span>}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>This syntax definitely looks more concise than a for loop and more elegant than the <code>map()<\/code> function.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='python-set-comprehension-with-an-if-clause-example'>Python Set comprehension with an if clause example <a href=\"#python-set-comprehension-with-an-if-clause-example\" class=\"anchor\" id=\"python-set-comprehension-with-an-if-clause-example\" title=\"Anchor for Python Set comprehension with an if clause example\">#<\/a><\/h2>\n\n\n\n<p>Suppose you want to convert all elements of the <code>tags<\/code> set to lowercase except for the <code>Numpy<\/code>. <\/p>\n\n\n\n<p>To do it, you can add a condition to the set comprehension like this:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">tags = {<span class=\"hljs-string\">'Django'<\/span>, <span class=\"hljs-string\">'Pandas'<\/span>, <span class=\"hljs-string\">'Numpy'<\/span>}\nnew_tags = {tag.lower() <span class=\"hljs-keyword\">for<\/span> tag <span class=\"hljs-keyword\">in<\/span> tags <span class=\"hljs-keyword\">if<\/span> tag != <span class=\"hljs-string\">'Numpy'<\/span>}\n\nprint(new_tags)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pythontutorial.net\/playground\/?q=dGFncyA9IHsnRGphbmdvJywgJ1BhbmRhcycsICdOdW1weSd9Cm5ld190YWdzID0ge3RhZy5sb3dlcigpIGZvciB0YWcgaW4gdGFncyBpZiB0YWcgIT0gJ051bXB5J30KCnByaW50KG5ld190YWdzKQ%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">{<span class=\"hljs-string\">'django'<\/span>, <span class=\"hljs-string\">'pandas'<\/span>}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='summary'>Summary <a href=\"#summary\" class=\"anchor\" id=\"summary\" title=\"Anchor for Summary\">#<\/a><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use Python set comprehension to create a new set based on an existing set by applying an expression to each element of the existing set.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='quiz'>Quiz <a href=\"#quiz\" class=\"anchor\" id=\"quiz\" 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