{"id":172,"date":"2018-04-30T12:48:21","date_gmt":"2018-04-30T10:48:21","guid":{"rendered":"http:\/\/pythonprogramming.altervista.org\/?p=172"},"modified":"2018-08-27T07:56:27","modified_gmt":"2018-08-27T05:56:27","slug":"lists-in-python-append-vs-extend-method","status":"publish","type":"post","link":"https:\/\/pythonprogramming.altervista.org\/lists-in-python-append-vs-extend-method\/","title":{"rendered":"Lists in Python: append vs extend method"},"content":{"rendered":"

Append vs Extend<\/h1>\n

Let’s discover how to change lists.<\/p>\n

What are lists in Python?<\/h2>\n

Lists are one of the fondamental tools of Python. They are what arrays are for other languages.<\/p>\n

You can create a list simply like this:<\/p>\n

mylist = [1,2,3]<\/strong><\/p><\/blockquote>\n

But you can put everything in a list: strings, objects… anything.<\/p>\n

names_list = [“John”, “Peter”, “Mary”]<\/strong><\/p><\/blockquote>\n

There are different ways to add elements to a list. Let’s take a look at\u00a0 them.<\/p>\n

Two different methods…<\/h2>\n
\n
\"which<\/a>
extend vs append<\/figcaption><\/figure><\/blockquote>\n

With append you can append a single element that will extend the list:<\/p>\n

>>><\/span> a <\/span>=<\/span> [<\/span>1<\/span>,<\/span>2<\/span>]<\/span>\r\n>>><\/span> a<\/span>.<\/span>append<\/span>(<\/span>3<\/span>)<\/span>\r\n>>><\/span> a\r\n<\/span>[<\/span>1<\/span>,<\/span>2<\/span>,<\/span>3<\/span>]<\/span><\/code><\/pre>\n
If you want to extend more than one element you should use extend, because you can only append one elment or one list of element:<\/p>\n
>>><\/span> a<\/span>.<\/span>append<\/span>([<\/span>4<\/span>,<\/span>5<\/span>])<\/span>\r\n>>><\/span> a\r\n<\/span>>>><\/span> [<\/span>1<\/span>,<\/span>2<\/span>,<\/span>3<\/span>,[<\/span>4<\/span>,<\/span>5<\/span>]]<\/span><\/code><\/pre>\n
So that you get a nested list<\/p>\n
Instead with extend you can extend a single element like this<\/p>\n
>>><\/span> a <\/span>=<\/span> [<\/span>1<\/span>,<\/span>2<\/span>]<\/span>\r\n>>><\/span> a<\/span>.<\/span>extend<\/span>([<\/span>3<\/span>])<\/span>\r\n>>><\/span> a\r\n<\/span>[<\/span>1<\/span>,<\/span>2<\/span>,<\/span>3<\/span>]<\/span><\/code><\/pre>\n
Or, differently from append, extend more elements in one time without nesting the list into the original one (that’s the reason of the name extend)<\/p>\n
>>><\/span> a<\/span>.<\/span>extend<\/span>([<\/span>4<\/span>,<\/span>5<\/span>,<\/span>6<\/span>])<\/span>\r\n>>><\/span> a\r\n<\/span>[<\/span>1<\/span>,<\/span>2<\/span>,<\/span>3<\/span>,<\/span>4<\/span>,<\/span>5<\/span>,<\/span>6<\/span>]<\/span><\/code><\/pre>\n
append 1 element<\/h2>\n
>>><\/span> x <\/span>=<\/span> [<\/span>1<\/span>,<\/span>2<\/span>]<\/span>\r\n>>><\/span> x<\/span>.<\/span>append<\/span>(<\/span>3<\/span>)<\/span>\r\n>>><\/span> x\r\n<\/span>[<\/span>1<\/span>,<\/span>2<\/span>,<\/span>3<\/span>]<\/span><\/code><\/pre>\n
extend one element<\/h2>\n
>>><\/span> x <\/span>=<\/span> [<\/span>1<\/span>,<\/span>2<\/span>]<\/span>\r\n>>><\/span> x<\/span>.<\/span>extend<\/span>([<\/span>3<\/span>])<\/span>\r\n>>><\/span> x\r\n<\/span>[<\/span>1<\/span>,<\/span>2<\/span>,<\/span>3<\/span>,<\/span>4<\/span>]<\/span><\/code><\/pre>\n
\n
Adding more elements… with different results<\/h1>\n<\/blockquote>\n
If you use append for more than one element, you have to pass a list of elements as arguments and you will obtain a NESTED list!<\/p>\n
>>><\/span> x <\/span>=<\/span> [<\/span>1<\/span>,<\/span>2<\/span>]<\/span>\r\n>>><\/span> x<\/span>.<\/span>append<\/span>([<\/span>3<\/span>,<\/span>4<\/span>])<\/span>\r\n>>><\/span> x\r\n<\/span>[<\/span>1<\/span>,<\/span>2<\/span>,[<\/span>3<\/span>,<\/span>4<\/span>]]<\/span><\/code><\/pre>\n
With extend, instead, you pass a list as argument, but you will obtain a list with the new element that are not nested in the old one.<\/p>\n
>>><\/span> z <\/span>=<\/span> [<\/span>1<\/span>,<\/span>2<\/span>]<\/span> \r\n>>><\/span> z<\/span>.<\/span>extend<\/span>([<\/span>3<\/span>,<\/span>4<\/span>])<\/span>\r\n>>><\/span> z\r\n<\/span>[<\/span>1<\/span>,<\/span>2<\/span>,<\/span>3<\/span>,<\/span>4<\/span>]<\/span><\/code><\/pre>\n
So, with more elements, you will use extend to get a list with more items. You will use append, to append not more elements to the list, but one element that is a nested list as you can clearly see in the output of the code.<\/p>\n
\"enter<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"Append vs Extend Let’s discover how to change lists. What are lists in Python? Lists are one of the fondamental tools of Python. \n [...]<\/a>","protected":false},"author":1,"featured_media":174,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_crdt_document":"","footnotes":""},"categories":[1,59],"tags":[62,61,60,29],"class_list":["post-172","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-examples","category-lists","tag-append","tag-extend","tag-list","tag-lists"],"avopt_banners_inside_post":true,"avopt_banners_on_page":true,"av_copy_from":"","av_sharing_message":"","av_sharing_allowed":false,"av_sharing_on":{"fb":[],"tw":[]},"av_allow_affiliate_banner":false,"av_allow_affiliate_multi_banner":false,"av_show_affiliation_buy_button":false,"av_post_rating":true,"av_have_post_rating_value":false,"av_is_artificial_intelligence_content":false,"_links":{"self":[{"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/posts\/172","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/comments?post=172"}],"version-history":[{"count":3,"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/posts\/172\/revisions"}],"predecessor-version":[{"id":176,"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/posts\/172\/revisions\/176"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/media\/174"}],"wp:attachment":[{"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/media?parent=172"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/categories?post=172"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/pythonprogramming.altervista.org\/wp-json\/wp\/v2\/tags?post=172"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\"enter<\/a><\/p>\n
Adding one element with both methods<\/h1>\n
\"enter<\/a><\/p>\n