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Asked: 2024-09-25T05:37:18+05:30 In:

How can I assign a value to a variable while checking a condition in a while loop in Python? I want to ensure that the assignment happens within the loop’s condition. What is the correct syntax for doing this?

I’ve been diving into Python and I hit a bit of a snag with while loops that involves variable assignments. So here’s the deal: I want to keep iterating through a while loop, but I also want to assign a value to a variable based on a condition inside that loop’s condition part. You know, like how you can often combine things to make your code cleaner and more efficient.

For example, I have this scenario where I want to keep asking a user for input until they give me a certain value, but I want to also assign that input value to a variable while I’m checking it in the loop. I’ve seen some examples where people do some crazy stuff with the while loop condition, and it looks kind of cool but honestly, I’m not sure how to wrap my head around it.

Let’s say I’m trying to get a user’s age, and I want to keep prompting them until they provide a valid age between 1 and 120. I want to do something like this:

“`python
while ( age := input(“Enter your age: “) ) not in range(1, 121):
print(“That’s not a valid age! Please try again.”)
“`

Is that how it’s supposed to go? Or am I totally off track here? I’ve heard that using the walrus operator `:=` can help with assignments in expressions, and I think that’s what I need, but I’m not quite sure if I’m using it correctly in this context.

Anyone out there have experience with this? I want my age variable to be updated with the latest input value during each iteration of the loop condition. Is the syntax I’m using correct, or is there a better way to handle this? Any insights would be super helpful—I really want to nail this down before moving on to other topics! Thanks in advance for your help!

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    2 Answers


    1. You’re definitely on the right track with using the walrus operator `:=`! It’s a nifty tool for assignment inside expressions, and it can definitely make your code cleaner.

      However, there’s a small hiccup in your syntax. The `input()` function returns a string, and the `range(1, 121)` function generates integers. To fix this, you’ll need to convert the input to an integer before checking if it’s in that range. Here’s how you can adjust your code:

      
while (age := int(input("Enter your age: "))) not in range(1, 121):
    print("That's not a valid age! Please try again.")

      But, the above code will throw an error if the user inputs something that’s not a number, because `int()` can’t convert it. So, you’ll want to handle that with a try-except block to catch those errors. It would look something like this:

      
while True:
    try:
        age = int(input("Enter your age: "))
        if age in range(1, 121):
            break
        else:
            print("That's not a valid age! Please try again.")
    except ValueError:
        print("That's not a valid number! Please try again.")

      In this version, you keep looping until the user gives you a valid age. If the input isn’t a number, it will print a different message telling them to try again. This way, you avoid crashing the program if they mess up the input. You’re definitely learning some cool stuff with Python loops! Keep it up!


    2. Using the walrus operator `:=` can indeed streamline your while loop when you want to assign a value to a variable during its conditional check. The syntax you are trying to use is almost there, but there’s a little adjustment needed. When capturing user input for age, the input function returns a string, so you should convert it to an integer before checking if it’s within the specified range. Additionally, the range needs to be checked if it falls within the bounds you defined. Here’s an improved version of your code:

      while (age := int(input("Enter your age: "))) not in range(1, 121):
    print("That's not a valid age! Please try again.")

      This snippet will prompt the user repeatedly until they enter a valid age between 1 and 120, updating the `age` variable with each iteration. Remember that if the input cannot be converted to an integer (like if the user inputs a non-numeric value), Python will raise a ValueError. To handle this more gracefully, you might want to wrap the input and conversion in a try-except block. This ensures your program doesn’t crash if an unexpected input is entered:

      while True:
    try:
        # Capturing and converting user input
        if (age := int(input("Enter your age: "))) in range(1, 121):
            break  # Exit loop if age is valid
        else:
            print("That's not a valid age! Please try again.")
    except ValueError:
        print("Please enter a valid number.")

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