{"id":6530,"date":"2018-11-20T04:52:36","date_gmt":"2018-11-20T04:52:36","guid":{"rendered":"https:\/\/www.jquery-az.com\/?p=6530"},"modified":"2018-11-20T04:52:36","modified_gmt":"2018-11-20T04:52:36","slug":"python-list-index","status":"publish","type":"post","link":"https:\/\/www.jquery-az.com\/python-list-index\/","title":{"rendered":"Python List Index Function"},"content":{"rendered":"<p>The index function searches a <a href=\"\/python-list-12-examples-to-learn-with-built-in-methods\/\">list<\/a> and returns the position of the first matched item in the specified list. For example:<\/p>\n<blockquote><p>Lst_index = list_name.index(&#8220;a&#8221;)<\/p><\/blockquote>\n<p><strong>A few points to be noted about the <a href=\"https:\/\/www.jquery-az.com\/python-list-12-examples-to-learn-with-built-in-methods\/\">Python List<\/a> Index function:<\/strong><\/p>\n<ul>\n<li>The index starts at zero.<\/li>\n<li>If there are more than one occurrences found for the searched value then index function returns the position of first matched element.<\/li>\n<li>If no element is found then a <strong>ValueError<\/strong> is raised.<\/li>\n<\/ul>\n<h3><strong>Syntax of list index function<\/strong><\/h3>\n<p>The general syntax for using the list index function is:<\/p>\n<blockquote><p>list.index(item_to_search)<\/p><\/blockquote>\n<h3><strong>A simple example of the list index function<\/strong><\/h3>\n<p>In this example, we have a list of five numeric elements. Then we used index function and searched for value \u201c10\u201d in the list. See what we get:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">#Python index function examples\r\n\r\n\r\n\r\nlst_num = [0, 5, 10, 15, 20, 25]\r\n\r\nint_pos = lst_num.index(10)\r\n\r\n\r\n\r\nprint (\"The position of item 10 = \", int_pos)<\/pre>\n<p><strong>The output of the above code is:<\/strong><\/p>\n<blockquote><p>The position of item 10 =\u00a0 2<\/p><\/blockquote>\n<h3><strong>The example of multiple occurrences<\/strong><\/h3>\n<p>In the list below, we have elements with multiple occurrences. The item \u201cA\u201d exists three times in the list and this is what we searched in the index function as well. See what index function returns:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">lst_str = [\"X\",\"B\",\"A\", \"D\",\"Z\", \"A\" ,\"C\",\"A\"]\r\n\r\nstr_pos = lst_str.index(\"A\")\r\n\r\n\r\n\r\nprint (\"Index of A = \", str_pos)<\/pre>\n<p><strong>The output:<\/strong><\/p>\n<blockquote><p>Index of A =\u00a0 2<\/p><\/blockquote>\n<p>You can see, the item \u201cA\u201d exists three times in the list, however, the index function returned the lowest index i.e. 2.<\/p>\n<h3><strong>What happens if a value is not found in the list?<\/strong><\/h3>\n<p>Now, let us search a term in the list that does not exist.<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">lst_animals = [\"cat\", \"dog\", \"cow\", \"bull\"]\r\n\r\n\r\n\r\nanimal_pos1 = lst_animals.index(\"cat\")\r\n\r\nanimal_pos2 = lst_animals.index(\"rat\")\r\n\r\n\r\n\r\nprint (\"Position of cat = \", animal_pos1)\r\n\r\nprint (\"Position of rat = \", animal_pos2)<\/pre>\n<p><strong>The result:<\/strong><\/p>\n<p><span style=\"color: #ff0000;\">\u00a0\u00a0\u00a0 animal_pos2 = lst_animals.index(&#8220;rat&#8221;)<\/span><\/p>\n<p><span style=\"color: #ff0000;\">ValueError: &#8216;rat&#8217; is not in list<\/span><\/p>\n<h3><strong>Specifying the start index example<\/strong><\/h3>\n<p>You may also specify the starting position in the <a href=\"\/python-list-12-examples-to-learn-with-built-in-methods\/\">Python list<\/a> for searching the index of an item. This is particularly useful for searching item with duplicate occurrences.<\/p>\n<p>In the following example, we have a few duplicate items in the list of strings. Then, index function is used to return the position of an item with the starting index argument:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">#index with start argument\r\n\r\n\r\n\r\nlst_fruits = [\"Apple\",\"Mango\",\"Strawberry\",\"Banana\",\"Apple\",\"Currant\"]\r\n\r\nfruit_pos = lst_fruits.index(\"Apple\", 2)\r\n\r\n\r\n\r\nprint (\"Index of Apple from position 2 = \", fruit_pos)<\/pre>\n<p><strong>The result of the above code is:<\/strong><\/p>\n<blockquote><p>Index of Apple from position 2 =\u00a0 4<\/p><\/blockquote>\n<p>Although, the first occurrence of the item \u201cApple\u201d is 0, however, as we provided <strong>start index<\/strong> 2 so the index function started searching the list from the second item. Therefore, we got the result 4 which is the second occurrence of the \u201cApple\u201d.<\/p>\n<h3><strong>The example of start and end indices<\/strong><\/h3>\n<p>Not only you may provide the starting position but to limit the searching a list, you may also specify ending index. If both arguments (start and end) are given then index function searches the value within that limit.<\/p>\n<p>If that searched item even exists in the given list but it is beyond the given limit then ValueError occurs.<\/p>\n<p>The example below shows using the start and end arguments:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">#index with start and end arguments\r\n\r\n\r\n\r\nlst_animals = [\"cat\", \"dog\", \"cow\", \"bull\", \"bat\", \"dog\", \"goat\", \"cow\"]\r\n\r\nani_pos = lst_animals.index(\"cow\", 3, 6)\r\n\r\n\r\n\r\nprint (\"The position of cow = \", ani_pos)<\/pre>\n<p><strong>The result is an error:<\/strong><\/p>\n<p><span style=\"color: #ff0000;\">\u00a0\u00a0\u00a0 ani_pos = lst_animals.index(&#8220;cow&#8221;, 3, 6)<\/span><\/p>\n<p><span style=\"color: #ff0000;\">ValueError: &#8216;cow&#8217; is not in list<\/span><\/p>\n<p>Even though the \u201ccow\u201d exists twice in the list but we provided 3 and 6 positions to search in the list. The first occurrence is 2 while the second is 7 which is not within the limit we specified in the index function, so the ValueError generated.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The index function searches a list and returns the position of first matched item in the specified list. &#8211; The index starts at zero<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[17],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v21.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>5 Examples to Learn Python List Index Function<\/title>\n<meta name=\"description\" content=\"The index function searches a list and returns the position of first matched item in the specified list. - The index starts at zero\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.jquery-az.com\/python-list-index\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"5 Examples to Learn Python List Index Function\" \/>\n<meta property=\"og:description\" content=\"The index function searches a list and returns the position of first matched item in the specified list. - 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