If/Else Elif and Lists in Python

If/Else statement

If/Else in any programming language is used to make a decision depending upon a particular condition. Just like in real life we make decisions, we have to also make decisions in programming. Let's see this with an example:-

Example 1: Write a program that accepts the user's age as input and determines whether the person is an adult or not.

age = int(input('Enter your age: '))

if (age >= 18):
    print('You are an adult')
else:
    print('You are not an adult')

Explanation:

• We first declare a variable called age with an input function to accept user input wrapped inside the int function. The input function is used to get input from the user and the int function is used to convert that value into a number.

• Then we wrote an if statement to check whether the user is 18 or above years of age. If yes, then "You are an adult" gets printed on the console. We have to specify a : (colon) after the if condition and give an indentation in the next line. Indentation is nothing but the extra white space which you see before the *print *statement in the above code.

• Finally, we have an else statement that will run in case if statement fails. In the above example, if the user turns out to be less than 18 years of age, "You are not an adult" will be printed on the console.

Elif statement

Elif statement in python is the substitute for the Else/If statement which is used in other programming languages. It is used to decide on multiple conditions. Let's learn it better with an example-

Example 2: Create a grading system that assigns various grades to the students depending upon the marks obtained

marks = int(input('Enter your marks: '))

if(marks >= 90):
  print('Grade A+')
elif(marks >= 80):
  print('Grade A')
elif(marks >= 70):
  print('Grade B')
elif(marks >= 60):
  print('Grade C')
elif(marks < 60):
  print('Grade D')

Explanation

• In the first line, we created an input function, wrapped it inside int() to convert the input marks into integers, and assigned them to the marks variable.
• Then there's an If statement to check whether the input marks are equal to or more than 90, if yes, Grade A+ will be printed on the console.
• After that, there are 4 Elif statements. Each statement has its own Grade.
• If marks are >=80, Grade A will be printed, Grade B for >=70, Grade C >= 60, and Grade D for marks <60.

Lists

List is a data structure in Python which allows you to store multiple items in one place. You can think of List as an alternative to Arrays in Python. There are multiple real world use cases for Lists. Ex- Storing books and movie names in books and movie recommendation websites.

# Let's print the name of various social media platforms
socials = ["Twitter", "Facebook", "Instagram"]
print(socials) #Expected output - ['Twitter', 'Facebook', 'Instagram']

Explanation

• We created a list with various social media platform names, assigned it to variable socials, and used the print() function to print it on the console.
• You have to always wrap the content of the list inside square brackets([ ])
• Just like arrays, each item in the list has its index position which starts from 0. In the above example, Twitter has position 0, Facebook 1, and Instagram 2.

You can also print an item from the list using its index position. In the above code change print(socials) to print(socials[1]) and you'll get Facebook as the printed result.

List Operations

1. Replacing an item

# Let's create a numbered list in ascending order
numbers = [1,2,3,5,5,6,7,8]
print(numbers) # Expected output - [1,2,3,5,5,6,7,8]
# As you can see, we stored 5 twice, let's fix it
numbers[3] = 4  #This code will replace the value stored at index 3 with 4
print(numbers) # Expected output - [1,2,3,4,5,6,7,8]
# Yayyyyy, we successfully changed the value of 5 stored at index 3 with 4

Explanation

• At first, we created an ascending numbered list with 5 appearing twice in the list, at indexes 3 and 4.
• To fix this issue, we wrote another code numbers[3] = 4. This will replace the value stored at index position 3 with 4. If you want to change the value of any other position, you can change 3 in numbers[3] with a different index number, like numbers[0], and number[1] and so on.

2. Concatenating multiple lists

In Python, it is possible to concatenate multiple lists with each other. Let's see this with an example-

# Let's create 2 numbered lists - 1 to 5 and 6 to 10
numbers = [1,2,3,4,5]
newnumbers = [6,7,8,9,10]
print(numbers+newnumbers) # Expected output - [1,2,3,4,5,6,7,8,9, 10]
# This happened because we added the newnumbers list to numbers list and printed the result.

Explanation

• We created 2 numbered lists with numbers 1-5 and 6-10 respectively.
• After that, we printed the combined result of the addition of both lists and got our combined result.

3. Multiplication of Lists

In Python, you can also perform multiplication operations on Lists. You cannot multiply lists with each other but you can multiply them with an integer to repeat the value a certain number of times.

# Let's create a numbered list with value 1 to 5
numbers = [1,2,3,4,5]
print(numbers*2) # Expected output - [1,2,3,4,5,1,2,3,4,5]
# We multiplied our list by 2 and got the same result values twice due to the multiplication.

Explanation

• We first created a numbers list with values of 1 to 5.
• After that, we printed the result of the numbers list multiplied by two and got the result [1,2,3,4,5,1,2,3,4,5] because of the multiplication.

4. Check the existence of an item

This is one of the most important operations of the list - To check whether a particular item is present in the list or not. Let's see this with an example-

# Let' create a list with a few sample colors
colors = ["Red", "Blue", "Orange", "Pink"]
# Now let's check whether the color "Purple" exists in the list or not.
print("Purple" in colors) # Returns false because "Purple" is not in our list.
# Now let's check whether "Blue" is present in our list or not
print("Blue" in colors) # Returns true because "Blue" is present in our list.

Explanation

• We first created a list of colors with color Red, Blue, Orange, and Pink
• Next, we check whether Purple exists in our list or not with the following code - print("Purple" in colors)
• We got the result as false because there is no "Purple" in our list. Next, we did the same thing with "Blue".
• This time got the result true because "Blue" is present in our list.

Conclusion

That's it for today's post and I will see you soon in another Python tutorial. This tutorial and all the future tutorials in this series are based on The Complete Python Masterclass. Check out this course if you want to learn Python in detail.

Happy Coding!