Python Tutorials
Python Introduction
Python Get Started
Python Syntax
Python Comments
Python Variables
Python Data Types
Python Casting
Python Strings
Python Booleans
Python Operators
Python Lists
Python Tuples
Python Sets
Python Dictionaries
Python If...Else
Python While Loops
Python For Loops
Python Functions
Python Lambda
Python Arrays
Python Classes/Objects
Python Inheritance
Python Iterators
Python Scope
Python Modules
Python Dates
Python Math
Python JSON
Python RegEx
Python PIP
Python Try..Except
Python User Input
Python String Formatting
Python File Handling
Python File Handling
Python Read Files
Python Create/Write Files
Python Delete Files
Python Modules
Python Numpy
Python Pandas
Python SciPy
Previous
Python Lists
mylist = ["apple", "banana", "cherry"]
List
The list is used to store multiple items in one place.
The list is one of 4 data types built into Python that are used to store data collections, the other 3 are Tuple, Set, and Dictionary, all with different capabilities and usage.
Listing is done using square brackets:
Example
Create a List:
thislist = ["apple", "banana", "cherry"]
print(thislist)
List Items
List items are unique, flexible, and allow duplicate values.
List items are displayed, first item has reference [0], second item referenced [1] etc.
Ordered
If we say the lists are separate, it means that the items have a specific order, and that order will not change.
When you add new items to the list, new items will be placed at the end of the list.
Note: There are other listing methods that will change the order, but generally: the order of things will not change.
Changeable
The list is flexible, which means we can change, add, and remove items from the list once they have been created.
Allow Duplicates
As lists are identified, lists may contain items of the same value:
Example
Lists allow duplicate values:
thislist = ["apple", "banana", "cherry", "apple", "cherry"]
print(thislist)
List Length
To determine how many items are listed, use the len() function:
Example
Print the number of items in the list:
thislist = ["apple", "banana", "cherry"]
print(len(thislist))
List Items - Data Types
List items can be for any type of data:
Example
String, int and boolean data types:
list1 = ["apple", "banana", "cherry"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]
The list may contain various types of data:
Example
A list with strings, integers and boolean values:
list1 = ["abc", 34, True, 40, "male"]
type()
From Python's point of view, lists are classified as 'data-bound':
<class 'list'>
Example
What is the data type of a list?
mylist = ["apple", "banana", "cherry"]
print(type(mylist))
The list() Cosntructor
It is also possible to use the list() builder when creating a new list.
Example
Using the list() constructor to make a List:
thislist = list(("apple", "banana", "cherry")) # note the double round-brackets
print(thislist)
Python Collections (Arrays)
There are four types of data collection in Python editing language:
- The list is a ordered and flexible collection. Allows duplicate members.
- Tuple is a ordered and unchanged collection. Allows duplicate members.
- Set is a random, unstable *, and unidentified collection. No duplicate members
- The dictionary is a ordered order ** and is flexible. No duplicate members.
* Set items do not change, but you can delete and / or add items whenever you wish.
** Starting with version 3.7 of Python, dictionaries are in order. In Python 3.6 and earlier, dictionaries are not organized.
When choosing a type of collection, it is helpful to understand the characteristics of that type. Choosing the right type of specific data set may mean keeping the definition, and, it may mean increased efficiency or security.
Python - Access List Items
Access Items
List items are displayed and you can access them by referring to the reference number:
Example
Print the second item of the list:
thislist = ["apple", "banana", "cherry"]
print(thislist[1])
Note: The first item has a 0 value.
Negative Indexing
Poor targeting means starting from the end
-1 refers to the last item, -2 refers to the last item etc.
Example
Print the last item of the list:
thislist = ["apple", "banana", "cherry"]
print(thislist[-1])
Range of Indexes
You can specify the width of the indicators by specifying where to start and where to end the width.
When you specify a range, the return value will be the new list containing the specified items.
Example
Return the third, fourth, and fifth item:
thislist = ["apple", "banana", "cherry", "orange",
"kiwi", "melon", "mango"]
print(thislist[2:5])
Note: Search will start in index 2 (included) and end in index 5 (not included).
Remember that the first item has a 0 value.
By excluding the original value, the range will start at the first item:
Example
This example returns the items from the beginning to, but NOT including, "kiwi":
thislist = ["apple", "banana", "cherry", "orange",
"kiwi", "melon", "mango"]
print(thislist[:4])
Excluding the last value, the range will continue to the end of the list:
Example
This example returns the items from "cherry" to the end:
thislist = ["apple", "banana", "cherry", "orange",
"kiwi", "melon", "mango"]
print(thislist[2:])
Range of Negative Indexes
Specify negative clues if you want to start a search from the end of the list:
Example
This example returns the items from "orange" (-4) to, but NOT including "mango" (-1):
thislist = ["apple", "banana", "cherry", "orange",
"kiwi", "melon", "mango"]
print(thislist[-4:-1])
Check if Item Exists
To determine if something is on the list, use a in keyword:
Example
Check if "apple" is present in the list:
thislist = ["apple", "banana", "cherry"]
if "apple" in thislist:
print("Yes, 'apple' is in the fruits list")
Python - Change List Items
Change item Value
To change the value of an item, see the reference number:
Example
Change the second item:
thislist = ["apple", "banana", "cherry"]
thislist[1] = "blackcurrant"
print(thislist)
Change a Range of Item Values
To change the value of items between a particular range, define a list with new values, and then specify a reference number range where you want to enter new values:
Example
Change the values "banana" and "cherry" with the values "blackcurrant" and "watermelon":
thislist = ["apple", "banana", "cherry", "orange", "kiwi", "mango"]
thislist[1:3] = ["blackcurrant", "watermelon"]
print(thislist)
If you enter more items than you change, new items will be added as you specify, and the remaining items will go accordingly:
Example
Change the second value by replacing it with two new values:
thislist = ["apple", "banana", "cherry"]
thislist[1:2] = ["blackcurrant",
"watermelon"]
print(thislist)
Note: The length of the list will change when the number of items included does not match the number of items changed.
If you enter smaller items than you replace, new items will be added as you specify, and the remaining items will go accordingly:
Example
Change the second and third value by replacing it with one value:
thislist = ["apple", "banana", "cherry"]
thislist[1:3] = ["watermelon"]
print(thislist)
Insert Items
To add a new list item, without adding any existing values, we can use the insert() method.
The insert() method inserts an object into a specified index:
Example
Insert "watermelon" as the third item:
thislist = ["apple", "banana", "cherry"]
thislist.insert(2, "watermelon")
print(thislist)
Note: As a result of the example above, the list will now contain 4 items.