Taking Conditional User Inputs - Python

Taking conditional user inputs means asking user for input and then checking it against certain conditions before accepting or processing it. This helps ensure that input is valid, meets specific rules or triggers different actions based on user's response. It's useful for creating interactive and error-free programs.

Example:

Below code takes user's age as input and uses an if-else condition to check if they are eligible (18 or older).

age = int(input("Enter your age: "))
if age >= 18:
    print("Eligible")
else:
    print("Not Eligible")

Output

Enter your age: 22
Eligible

Types of Conditional User Inputs

There are different ways to take conditional input in Python depending on what is being checked. Let's look at the most common types:

1. Using if and else Conditions

It is the most basic form of conditional input. After receiving input from user, programmer uses an if statement to check a condition and provides different responses based on whether condition is true or false.

Example:

This program checks if entered number is positive or not using a simple if-else condition.

num = int(input("Enter a number: "))
if num > 0:
    print("Positive Number")
else:
    print("Not Positive Number")

Output

Enter a number: 12
Positive Number

2. Using if, elif and else Conditions

This allows programmer to check multiple conditions. The program goes through each condition one by one and runs the first one that is true.

Example:

Below code takes marks as input and uses if-elif-else conditions to assign a grade based on the score.

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

if marks >= 90:
    print("Grade A")
elif marks >= 75:
    print("Grade B")
elif marks >= 60:
    print("Grade C")
else:
    print("Grade D")

Output

Enter your marks: 98
Grade A

3. Using Nested if Conditions

Nested if conditions are used when a decision depends on multiple layers of checks. After first condition is true, program checks another condition inside it. This helps handle more detailed or specific user input situations.

Example:

Here, program checks the username and password using nested if statements and prints a login result based on input.

username = input("Enter username: ")
password = input("Enter password: ")

if username == "admin":
    if password == "1234":
        print("Login successful.")
    else:
        print("Incorrect password.")
else:
    print("Unknown username.")

Output

Enter username: admin
Enter password: 1234
Login successful.

4. Using while Loop for Repeated Input

When a program needs to ask user for input multiple times especially until they give a valid response a while loop is very useful. It keeps running and asking for input until a certain condition is met.

Example:

This program keeps asking user to enter correct password using a while loop. It only stops when user types "python123", then it prints "Access granted!".

password = ""
while password != "python123":
    password = input("Enter the password: ")

print("Access granted!")

Output

Enter the password: python
Enter the password: python1
Enter the password: python123
Access granted!

5. Using try-except for Valid Input Type

try-except helps handle input errors. If the user enters wrong type (like text instead of a number), try-except catches error and lets the program continue without crashing.

Example:

In this Example, a while loop is used with try-except to safely take user's age. It keeps asking until a valid number is entered preventing program from crashing on invalid input.

while True:
    try:
        age = int(input("Enter your age: "))
        break
    except ValueError:
        print("Invalid input! Please enter a number.")

print("Thank you! You entered:", age)

Output

Enter your age: abc
Invalid input! Please enter a number.
Enter your age: 18
Thank you! You entered: 18

Related Articles:

• Conditional statement in Python
• if-else statement
• while loop
• try-except block
• Nested if Statement