{"id":33,"date":"2020-11-03T05:37:23","date_gmt":"2020-11-03T05:37:23","guid":{"rendered":"http:\/\/www.bhargaviurs.com\/?p=33"},"modified":"2025-04-21T13:49:11","modified_gmt":"2025-04-21T13:49:11","slug":"list-comprehensions","status":"publish","type":"post","link":"https:\/\/www.bhargaviurs.com\/index.php\/2020\/11\/03\/list-comprehensions\/","title":{"rendered":"List comprehensions"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Here is a simple python for loop: <\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">list_i = []\nfor i in range(5):\n    list_i.append(i)<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">Notice that append() function is called to add elements to the list. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Let&#8217;s write the same using List comprehension:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">list_i = [i for i in range(5)]<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">The simplest way to understand why list comprehensions are faster is by noticing that in the first example, append() function is called explicitly. But in list comprehension, it is in-built. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">for loop time = time taken for looping + executing append() function<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">list comprehension = built-in looping and building a list <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Some more examples of list comprehensions:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>Square of a number. <\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">list_i = [i*i for i in range(5)]<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\"><li>Subtract each number by a given number 10<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">list_i = [10-i for i in range(5)]<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\"><li>Add 5 to each number. <\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">list_i = [i + 5 for i in range(5)]<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Introducing conditions in list comprehensions.<\/h3>\n\n\n\n<ul class=\"wp-block-list\"><li>Even numbers between 1 to 20<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">list_i = [i for i in range(1,21) if i % 2 == 0]<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\"><li>Return even numbers given a list of numbers. <\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">numbers = [2,1,4,5,3,9,10,24,36,72,88]\n\nlist_i = [i for i in numbers if i % 2 == 0]<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">Using Dictionaries in List comprehensions<\/h3>\n\n\n\n<ul class=\"wp-block-list\"><li>Given a dictionary, find all keys whose value is &#8216;3&#8217; <\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">a = {'a': 3, 'b': 2, 'c': 3, }\n\nkeys = [k for k, v in a.items() if v == 3]<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\"><li>Given a dictionary where value of key is a list, find all keys that has &#8216;5&#8217; in it&#8217;s value.<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"python\" class=\"language-python\">a = {1: [2,4,6],\n     2: [5,6,7],\n     6: [8,9,5]}\n\nprint [k for k, v in a.items() if 5 in a[k]]<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Here is a simple python for loop: Notice that append() function is called to add elements to the list. Let&#8217;s write the same using List comprehension: The simplest way to understand why list comprehensions are faster is by noticing that in the first example, append() function is called explicitly. But in list comprehension, it is &hellip; <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-33","post","type-post","status-publish","format-standard","hentry","category-uncategorized","entry"],"_links":{"self":[{"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/posts\/33","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/comments?post=33"}],"version-history":[{"count":18,"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/posts\/33\/revisions"}],"predecessor-version":[{"id":52,"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/posts\/33\/revisions\/52"}],"wp:attachment":[{"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/media?parent=33"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/categories?post=33"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bhargaviurs.com\/index.php\/wp-json\/wp\/v2\/tags?post=33"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}