In this article, let\u2019s learn about Python Lists.<\/p>\n
List is one of the most powerful<\/strong> data structures in Python. The List data type is made with so much of efforts and every programmer from beginner<\/strong>, intermediate<\/strong> to an expert<\/strong> should understand how it works.<\/p>\n So let\u2019s go ahead and dive into the lists.<\/p>\n Python does not have arrays<\/strong> like Java<\/strong> or C++<\/strong>. Arrays are data structures which hold multiple values<\/strong>.<\/p>\n Python does not have arrays but it has lists<\/strong>. Lists are mutable collections<\/strong> of objects<\/strong>.<\/p>\n This is an example:<\/p>\n You can create lists in many ways:<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n You can use the in-built list() function<\/strong> to convert another data type<\/strong> into a list<\/strong>. It can also create an empty list<\/strong> without parameters<\/strong>.<\/p>\n Like strings, we can index lists<\/strong> to access their values<\/strong>. Indexing starts at 0<\/strong>.<\/p>\n Let\u2019s take an example.<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n 12 is the value at index 2.<\/p>\n Indexing left to right<\/strong>, starts at 0<\/strong>.<\/p>\n Output:<\/strong><\/p>\n Indexing right to left<\/strong>, starts at -1<\/strong>.<\/p>\n Output:<\/strong><\/p>\n We can slice lists as well. This gives us only a part<\/strong> of the list. Slicing can take one, two or three values – start<\/strong>, stop<\/strong> and step<\/strong>.<\/p>\n Let\u2019s take examples here as well.<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Unlike strings, lists are mutable<\/strong>. You can change its values<\/strong>.<\/p>\n Let us take a few examples.<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n values[1] is now \u2018bread\u2019 and not \u2018cheese\u2019.<\/p>\n Output:<\/strong><\/p>\n If we assign this list to the slice values[1:1]<\/strong>, it adds the values \u2018cheese\u2019 and \u2018eggs\u2019 between indices 0<\/strong> and 1<\/strong>.<\/p>\n Lists are mutable<\/strong>, so we can also add elements later. We can do this in many ways.<\/p>\n We can append values to the end<\/strong> of the list. We use the append()<\/strong> method for this. You can use this to append single values to the list – value<\/strong>, list<\/strong>, tuple<\/strong>.<\/p>\n Output:<\/strong><\/p>\n You can insert values in a list with the insert() method<\/strong>. Here, you specify a value to insert at a specific position<\/strong>.<\/p>\n Output:<\/strong><\/p>\n extend() can add multiple<\/strong> items to a list.<\/p>\n Learn by example:<\/p>\n Output:<\/strong><\/p>\n Lists have methods for deleting elements. They are remove()<\/strong> and pop()<\/strong> and are slightly different from each other.<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Here in this example, we say we want to remove the value 2 from this list.<\/p>\n It removes the first occurrence<\/strong> of 2 at index 1 but does not remove the second one<\/strong> at index 3. By default, pop()<\/strong> removes the last element<\/strong> in the list. You cannot remove an element that is not in the list<\/strong>.<\/p>\n Output:<\/strong><\/p>\n We can also give pop()<\/strong> and index to make it remove<\/strong> an element from a specific index<\/strong>.<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Since lists are collections<\/strong> of elements<\/strong>, we can use them in for-loops. You can do this if you want to do something for every value<\/strong> in a list.<\/p>\n Code:<\/strong><\/p>\n Output:<\/strong><\/p>\n Code:<\/strong><\/p>\n Output:<\/strong><\/p>\n Like for strings, we can calculate the length<\/strong> of a list<\/strong>. For this, we use the in-built len() function<\/strong>.<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n We can join two lists with the + operator<\/strong>. It adds<\/strong> integers<\/strong> and floats<\/strong> but concatenates strings<\/strong> and lists<\/strong>.<\/p>\n Output:<\/strong><\/p>\n We can make a list repeat<\/strong> by multiplying<\/strong> it by an integer<\/strong>. We saw this in strings.<\/p>\n Output:<\/strong><\/p>\n And we can also check whether a value<\/strong> is in a list. For this, we use the in operator<\/strong>.<\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n Output:<\/strong><\/p>\n The list class has an in-built copy() method<\/strong> which creates a copy<\/strong> of a list.<\/p>\nWhat are Python Lists?<\/h3>\n
values=['milk','cheese',12, False]<\/pre>\n
\n
Creating Lists in Python<\/h3>\n
>>> items=[1,2,3]\n>>> items<\/pre>\n
>>> items=list('123')\n>>> items<\/pre>\n>>> items=['123']\n>>> items<\/pre>\n
>>> items=[]\n>>> items.append(7)\n>>> items<\/pre>\n
>>> items=[1, 2, False, [4, 5]]\n>>> items<\/pre>\n
Indexing Lists in Python<\/h3>\n
>>> values<\/pre>\n
>>> values[2]<\/pre>\n
1. Positive Indexing<\/h4>\n
>>> values[1]<\/pre>\n
2. Negative Indexing<\/h4>\n
>>> values[-1]<\/pre>\n
Slicing Lists in Python<\/h3>\n
>>> values #list<\/pre>\n
>>> values[:] #complete list<\/pre>\n
>>> values[:2] #upto index 1<\/pre>\n
>>> values[2:] #from index 2 to end<\/pre>\n
>>> values[-3:] #from index -3 to end<\/pre>\n
>>> values[1::2] #from index 1 to end with a step of 2<\/pre>\n
Modifying Lists in Python<\/h3>\n
>>> values<\/pre>\n
>>> values[1]='bread'\n>>> values<\/pre>\n
>>> values[1:1]=['cheese','eggs']\n>>> values<\/pre>\n
Adding Elements in Python Lists<\/h3>\n
1. append()<\/h4>\n
>>> nums=[1,2,3]\n>>> nums.append(4)\n>>> nums.append([5,6])\n>>> nums.append((7,8))\n>>> nums<\/pre>\n
2. insert()<\/h4>\n
>>> nums=[1,2,3]\n>>> nums.insert(2,4)\n>>> nums<\/pre>\n
3. extend()<\/h4>\n
>>> nums=[1,2,3]\n>>> nums.extend([[4,5,6],(7,8),9])\n>>> nums<\/pre>\n
Deleting Elements in Python Lists<\/h3>\n
>>> nums=[1,2,3,2,4,5,3,6,7,8]\n>>> nums.remove(2)\n>>> nums<\/pre>\n
>>> nums.pop()<\/pre>\n
>>> nums.pop()<\/pre>\n
>>> nums.remove(0)<\/pre>\n
\n\u00a0\u00a0<\/b>File “<pyshell#148>”, line 1, in <module>
\n\u00a0\u00a0\u00a0\u00a0<\/b>nums.remove(0)
\nValueError: list.remove(x): x not in list<\/div>\n>>> nums<\/pre>\n
>>> nums.pop(5)<\/pre>\n
>>> nums<\/pre>\n
Looping on Lists in Python<\/h3>\n
for num in [1,2,3,4,5,6]: \n print(num)<\/pre>\n
\n2
\n3
\n4
\n5
\n6<\/div>\nnums=[1,2,3,4,5,6]\nfor index in range(len(nums)):\n print(nums[index])<\/pre>\n
\n2
\n3
\n4
\n5
\n6<\/div>\nPython Lists Length<\/h3>\n
>>> nums=[1,2,3,4,5]\n>>> len(nums)<\/pre>\n
for index in range(len(nums)):\n print(index,nums[index])<\/pre>\n
\n1 2
\n2 3
\n3 4
\n4 5<\/div>\nConcatenating, Repetition and Membership<\/h3>\n
>>> [1,2,3]+[4,5]+[6]<\/pre>\n
>>> [1,2,3]*3<\/pre>\n
>>> [1,2] in [1,2,3]<\/pre>\n
>>> 2 in [1,2,3]<\/pre>\n
>>> '' not in []<\/pre>\n
Copying Lists in Python<\/h3>\n
>>> nums=[1,2,3,4]\n>>> nums1=nums.copy()\n>>> nums1<\/pre>\n