Lists are used to store multiple items in a single variable.
Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary, all with different qualities and usage.
Lists are created using square brackets:
ExampleCreate a List:
thislist = ["apple", "banana", "cherry"]print(thislist)Try it Yourself »List ItemsList items are ordered, changeable, and allow duplicate values.
List items are indexed, the first item has index [0],the second item has index [1] etc.
OrderedWhen we say that lists are ordered, it means that the items have a defined order, and that order will not change.
If you add new items to a list,the new items will be placed at the end of the list.
Note: There are some list methods that will change the order, but in general: the order of the items will not change.
ChangeableThe list is changeable, meaning that we can change, add, and remove items in a list after it has been created.
Allow DuplicatesSince lists are indexed, lists can have items with the same value:
ExampleLists allow duplicate values:
thislist = ["apple", "banana", "cherry", "apple", "cherry"]print(thislist)Try it Yourself »List LengthTo determine how many items a list has, use the len() function:
ExamplePrint the number of items in the list:
thislist = ["apple", "banana", "cherry"]print(len(thislist))Try it Yourself »List Items - Data TypesList items can be of any data type:
ExampleString, int and boolean data types:
list1 = ["apple", "banana", "cherry"]list2 = [1, 5, 7, 9, 3]list3 = [True, False, False]Try it Yourself »A list can contain different data types:
ExampleA list with strings, integers and boolean values:
list1 = ["abc", 34, True, 40, "male"]Try it Yourself »type()From Python's perspective, lists are defined as objects with the data type 'list':
ExampleWhat is the data type of a list?
mylist = ["apple", "banana", "cherry"]print(type(mylist))Try it Yourself »The list() ConstructorIt is also possible to use the list() constructor when creating a new list.
ExampleUsing the list() constructor to make a List:
thislist = list(("apple", "banana", "cherry")) # note the double round-bracketsprint(thislist)Try it Yourself »Python Collections (Arrays)There are four collection data types in the Python programming language:
List is a collection which is ordered and changeable. Allows duplicate members.Tuple is a collection which is ordered and unchangeable. Allows duplicate members.Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.Dictionary is a collection which is ordered** and changeable. No duplicate members.*Set items are unchangeable, but you can remove and/or add itemswhenever you like.
**As of Python version 3.7, dictionaries are ordered.In Python 3.6 and earlier, dictionaries are unordered.
When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.
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