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| Introduction | Variables | If-else |
| Strings | Functions | while-loop |
| For-Loop | List | Set |
| Dictionary | Tuple | Try..Except |
| Class/Object | Inheritance | Polymorphism |
| File Handling | ||
In Python, the List is one of the most common data structures you’ll come across. It shows up in almost every Python project, whether you’re building a website, analyzing data, or making a game, whenever you need to keep track of a group of items. List refers to a collection of data items which are normally related. Instead of storing these data as seperate variables, we can store them as a list. For example, if you need to store grdes of 5 students,
instead of storing them in studentGrade1, studentGrade2,studentGrade3, we can store them in a list.
A list has order, which means the items stay in the same sequence as you add them.
It’s also changeable, so you can add, remove, or modify items even after the list is created.
To make a list, just put your values inside square brackets [], and separate them with commas.
You can use the append() method to add an item to the end, or insert() to put an item in a specific spot.
If you want to add the item to the List at a specific position, just use the insert command. Let's see some code examples.
Code Example 1: #Creates a list listNames = ["John", "Joseph", "Jack"] #Print print(listNames) #Output: ['John', 'Joseph', 'Jack'] Code Example 2A: #Create List using append. listStates = [] listStates.append["Arizona"] listStates.append["Kansas"] listStates.append["Nevada"] #Print print(listStates) #Output: ['Arizona', 'Kansas', 'Nevada'] Code Example 2B: #Create List using list(). listColor = list() listColor.append["Green"] listColor.append["Blue"] listColor.append["Red"] #Print print(listColor) #Output: ['Green', 'Blue', 'Red'] Code Example 3: #Create list from tuple using list(). tuple1 = (10, 20, 30) list_from_tuple = list(tuple1) #Print print(list_from_tuple) #Output: [10,20,30] Code Example 4: #Create list from another list. list1 = ["Dublin","Fremont","Newark"] list_from_another_list = list(list1) #Print print(list_from_another_list ) #Output: ["Dublin","Fremont","Newark"] Code Example 5: #insert the item at a given position. listStates.insert(1,"Texas") #Print print(listStates) #Output: ['Arizona', 'Texas', 'Utah', 'Nevada']
When you assign one list to another, it does not create a new list. It creates a new reference to the same list object in memory. Python.
Code Example 6: #Creates a list list_A = [10, 20, 30] #list_A refers to same object as list_B list_B = list_A list_A.append(4) #Print print(list_A) print(list_B) #Output: [10, 20, 30, 4] [10, 20, 30, 4]
To update the items in the list, just assign a new value by refering to the index number.
Code Example 7:
#Creates a list
listCities = []
listCities.append("Chicago")
listCities.append("Houston")
listCities.append("Austin")
#Change the item "Dallas" to Phoenix,
listCities[1]="Phoenix"
#Print
print(listCities)
#Output:
['Chicago', 'Phoenix', 'Austin']
To remove the item from the list, use the remove method. You can also remove one or more items in the list using del. The syntax is del listName[index of item to be deleted]. You can use pop to remove an item from the list and get its value.
Code Example 8:
#Creates a list
listCities = []
listCities.append("Fremont")
listCities.append("Stockton")
listCities.append("Turlock")
listCities.append("Newark")
#Remove an item using remove
listCities.remove("Stockton")
#Print
print(listCities)
#Output:
['Fremont', 'Turlock', 'Newark']
Code Example 9:
#Remove item using del
del listCities[1]
#Print
print(listCities)
#Output:
['Fremont', 'Newark']
Code Example 10:
#Remove items using del
del listCities[2:4]
#Print
print(listCities)
Output:
['San Francisco', 'Fremont', 'Newark']
To find the length of the List, use the len method. Length of the list refers to the number of items in a list. The empty list will have 0 length. and the list with 10 items will have a length 10. If listA contains another list of 10 items, then the length of listA will be only 1.
Code Example 11: #Creates a list listColors = ['Green', 'Blue', 'Yellow'] #length of List x=len(listColors) #Print print(listColors) #Output: 3 Code Example 12: #List containing another list listA=['A', 'B', [1,2,3]] print(len(listA)) #Print print(listA) #Output: 3
For loop can be used to loop through the List.
#Creates a list listFruits = ["Banana", "Orange", "Apple"] #Loop through the list for x in listFruits: print(x) #Print print(listFruits) #Output: Banana Orange Apple
You can use the index number to access item/items in the List.
#Creates a list listFruits=["Banana","Orange","Apple","Grapes"] #To access "Orange" in the List x=listFruits[1] #Print print(x) #Output: Orange #To access "Grapes" in the List x=listFruits[3] #Print print(x) #Output: Grapes To access the last item of the List x=listFruits[-1] #Print print(x) #Output: Grapes #To access the 2nd last item of the List x=listFruits[-2] #Print print(x) #Output: Apple #To access the 2nd and 3rd items of the List x=listFruits[1:3] #Print print(x) #Output: ['Orange', 'Apple'] Get all the fruits except Banana x=listFruits[1:] #Print print(x) #Output: ['Orange', 'Apple', 'Grapes'] All items except last 2 items. x=listFruits[:-2] #Print print(x) #Output: ['Banana', 'Orange']
Use + operator to join 2 Lists..
#Creates a list list1 = ["Honda", "Toyota", "Lexus"] list2 = [1,2,3,4] #Add 2 Lists with + operator. list3=list1 + list2 #Print print(list3) #Output: ['Honda', 'Toyota', 'Lexus', 1, 2, 3, 4]
Lists can be sorted using the sort() method. To sort in descending order, pass the reverse = True argument. Use sorted() if you want a new sorted list to be created without changing the original list
#Creates a list listCities = ["middletown", "chicago", "phoenix"] #Sort listCities.sort() #Print print(listCities) #Output: ['chicago', 'middletown', 'phoenix'] #To sort the the descending order. list1.sort(reverse=True) #Print print(list1) #Output: ['phoenix', 'middletown', 'chicago'] #Create a list myList=[1,7,6,5] sortedList=sorted(myList) #Print print(myList) print(sortedList) #Output: [1,7,6,5] [1,5,6,7]
You can copy List into another List variable using copy() or list() method.
#Creates a list listCars1 = ["Honda", "Toyota", "Lexus"] #Copy to another List listCars2 listCars2 = listCars1.copy() #Print print(listCars2) Output: ['Honda', 'Toyota', 'Lexus'] Copy the list using list() method. listCars2=list(listCars1) #Print print(listCars2) Output: ['Honda', 'Toyota', 'Lexus']
The extend() method in list is used to add all the items from another list, tuple, set, or string to the end of the current list.
#Creates a list listCars = ["Honda"] #Copy to another List listCars2 listCarsNew = ["Ford"] listCars.extend(listCarsNew ) #Print print(listCars) Output: ['Honda', 'Ford']