List, Sort, Reverse, Adding, removing & modifying elements of List

 

PYTHON 

COMMENT

Comments are an extremely useful feature in most programming languages. Everything you’ve written in your programs so far is Python code. As your programs become longer and more complicated, you should add notes within your programs that describe your overall approach to the problem you’re solving. A comment allows you to write notes in English within your programs.

How to write comment

In Python, the hash mark (#) indicates a comment. Anything following a hash mark in your code is ignored by the Python interpreter.

For example:

#This is comment line

LIST:

A list is a collection of items in a particular order. You can make a list that includes the letters of the alphabet, the digits from 0–9, or the names of all the people in your family. You can put anything you want into a list, and the items in your list don’t have to be related in any particular way.

In Python, square brackets ([]) indicate a list, and individual elements in the list are separated by commas.

Example

Color=[‘blue’,’red’,’yellow’,’black’]

print(Color)

Run and See the output

Accessing Element of List

print(Color[0])

output will be ‘blue’

Meanwhile you can apply methods here

print(Color[0].title())

output: Blue (First letter of blue is capital now)

 

Python has a special syntax for accessing the last element in a list. By asking for the item at index -1, Python always returns the last item in the list:

print(Color[-1])

Output: black

This code returns the value 'specialized'. This syntax is quite useful, because you’ll often want to access the last items in a list without knowing exactly how long the list is. This convention extends to other negative index values as well. The index -2 returns the second item from the end of the list, the index -3 returns the third item from the end, and so forth.

Try to compose this message to use only one value from the list

Color=[‘blue’,’red’,’yellow’,’black’]

Message=”I have “+Color[1]+” Shirt”

Print(Message)

Changing, Adding and Removing Elements

Modifying Elements in the list

Color=[‘blue’,’red’,’yellow’,’black’]

print(Color)

Color[0]=’violet’

print(Color)

Now Output Will Be : violet, red, yellow, black

You can change the value of any item in a list, not just the first item.

Adding Elements to the list

Appending Elements to the End of the list

Mobile=[‘apple’,’techno’,’samsung’]

Print(Mobile)

Mobile.append(‘vivo’)

Print(Mobile)

Output: apple, techno, samsung, vivo

 

You add in Empty list

Car=[]

Car.append(‘BMW’)

Car.append(‘Audi’)

Car.append(‘Mercedes’)

print(Car)

output: [‘BMW’, ‘Audi’, ‘Mercedes’]

Removing Elements from the list

Removing an items using the del statement

Bike=[‘honda’,’hero’,’suzuki’]

print(Bike)

del Bike[0]

print(Bike)

Output: [‘hero’,’suzuki’]

Removing items using pop() Methods

Sometimes you’ll want to use the value of an item after you remove it from a list. For example, you might want to get the x and y position of an alien that was just shot down, so you can draw an explosion at that position. In a web application, you might want to remove a user from a list of active members and then add that user to a list of inactive members. The pop() method removes the last item in a list, but it lets you work with that item after removing it. The term pop comes from thinking of a list as a stack of items and popping one item off the top of the stack. In this analogy, the top of a stack corresponds to the end of a list.

Bike=[‘honda’,’hero’,’suzuki’]

print(Bike)

popped_Bike=Bike.pop()

print(Bike)

print(popped_Bike)

 

 

Output:

[‘honda’,’hero’,’suzuki’]

[‘honda’,’hero’]

[‘suzuki’]

You can pop any element using index number

Removing Items by value

Bike=[‘honda’,’hero’,’suzuki’]

Bike.remove(‘hero’)

print(Bike)

Output: [‘honda’,’suzuki’]

Sort() Method

Python’s sort() method makes it relatively easy to sort a list. Imagine we have a list of cars and want to change the order of the list to store them alphabetically. To keep the task simple, let’s assume that all the values in the list are lowercase.

cars = ['bmw', 'audi', 'toyota', 'subaru']

cars.sort()

print(cars)

Output: ['audi', 'bmw', 'subaru', 'toyota']

You can also sort this list in reverse alphabetical order by passing the argument reverse=True to the sort() method. The following example sorts the list of cars in reverse alphabetical order:

cars = ['bmw', 'audi', 'toyota', 'subaru']

cars.sort(reverse=True)

print(cars)

Again, the order of the list is permanently changed:

['toyota', 'subaru', 'bmw', 'audi']

Sorted() for Temporarily

cars = ['bmw', 'audi', 'toyota', 'subaru']

print(cars)

print(sorted(cars))

print(cars)

Output:

 ['bmw', 'audi', 'toyota', 'subaru']

 ['audi', 'bmw', 'subaru', 'toyota']

 ['bmw', 'audi', 'toyota', 'subaru']

Finding the Length of a List

You can quickly find the length of a list by using the len() function. The list in this example has four items, so its length is 4:

cars = ['bmw', 'audi', 'toyota', 'subaru']

len(cars)

4

Printing List in reverse order

cars = ['bmw', 'audi', 'toyota', 'subaru']

print(cars)

cars.reverse()

print(cars)

Output:

['bmw', 'audi', 'toyota', 'subaru']

[‘subaru’,’toyota’,’audi’,’bmw’]