What Python3 method can I use to restrict input to only integer in my assignment?

Question

I have a very brief familiarity with coding in general, though a majority of my experience thus far has been with Python. Which is why it's upsetting that I can't seem to figure out how to do this...

I have an assignment in my Python class where I am required to compute the area of a right triangle. I have completed the assignment successfully, but I wanted to take it a step further and restrict the user from inputting anything but an integer as input. I've tried multiple ideas from what I learned on Codecademy, though I can't seem to figure it out. Any help would be greatly appreciated!

Here is the code I've written so far; it works fine for what it is, but I would like to have it return a string that says something like "Please enter a valid number" if the user were to type anything besides a number:

from time import sleep
import math

print("Let\'s find the area of a right triangle!")
sleep(2)

triangleBase = float(input("Enter the base value for the triangle: "))
print("Great!")

triangleHeight = float(input("Enter the height value for the triangle: "))
print("Great!")
sleep(2)

print("Calculating the area of your triangle...")
sleep(2)

def triangleEquation():
    areaString = str("The area of your triangle is: ")
    triangleArea = float(((triangleBase * triangleHeight) / 2))
    print('{}{}'.format(areaString, triangleArea))

triangleEquation()

I really don't know enough about this sort of stuff in general... Hence the need for a class. Is there another way to capture user input then that would allow what I seek? — therealjayvi
– therealjayvi, Commented Apr 13, 2017 at 4:25
Check this... How can I limit the user input to only integers in Python — Taku
– Taku, Commented Apr 13, 2017 at 4:26

tdelaney · Accepted Answer · 2017-04-13 04:34:53Z

1

You are close. You noticed that your code raised an exception. All you need to do is catch that exception and prompt again. In the spirit of "don't repeat yourself", that can be its own function. I cleanup up a couple of other things, like your calculation function using global variables and converting things that don't need converting (e.g. 'foo' is a str, you don't need str('foo')) and got

from time import sleep
import math

def input_as(prompt, _type):
    while True:
        try:
            # better to ask forgiveness... we just try to return the
            # right stuff
            return _type(input(prompt.strip()))
        except ValueError:
            print("Invalid. Lets try that again...")

def triangleEquation(base, height):
    area = base * height / 2
    print('The area of your triangle is: {}'.format(areaString, area))


print("Let\'s find the area of a right triangle!")
sleep(2)

triangleBase = input_as("Enter the base value for the triangle: ", float)
print("Great!")

triangleHeight = input_as("Enter the height value for the triangle: ", float)
print("Great!")
sleep(2)

print("Calculating the area of your triangle...")
sleep(2)

triangleEquation(triangleBase, triangleHeight)

answered Apr 13, 2017 at 4:34

tdelaney

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2 Comments

therealjayvi Over a year ago

Thank you! This is exactly what was needed! So it would seem I need to become familiarized with how to use Try and Except. This worked perfectly for what was needed :)

tdelaney Over a year ago

There is a theory in python called duck-typing that says your code should assume operations are going to work and to catch exceptions when everything blows up in your face.

GH05T · Accepted Answer · 2017-04-13 04:33:40Z

0

This should get you started. I'll leave the rest for you (if you'd like to also allow floats, hint, hint), since you said you wanted to take it a step further, that way you'll still retain the sense of accomplishment.

def triangleEquation(triangleBase, triangleHeight):
    if type(triangleHeight) == int and type(triangleBase) == int:
        areaString = "The area of your triangle is: "
        triangleArea = float(((triangleBase * triangleHeight) / 2))
        return '{}{}'.format(areaString, triangleArea)
    else:
        return 'Integers only.'

Note: You could also use the is idiom: if type(triangleHeight) is int...

edited Apr 13, 2017 at 4:33

answered Apr 13, 2017 at 4:28

GH05T

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8 Comments

therealjayvi Over a year ago

I wish I had enough rep to be able to upvote your answer, your answer really helped open my eyes to new terms and concepts that I will definitely now begin looking into!

GH05T Over a year ago

Thanks. It's good that you wanted to take the solution to the problem a step further. That's a good habit to get into. I hope you enjoy programming with Python. I do! Good luck! Also, notice that I took your call to the print() function out of the triangleEquation() function. That's another good habit to get into: making your functions "fruitful" (having a return value other than None which is the default if nothing is returned, and is considered a void function. Then do your printing elsewhere, in the main() function.

GH05T Over a year ago

Here's a resource I found useful when I first started with Python, which was only a couple of months ago; it was one of the books recommended on python.org: openbookproject.net/thinkcs/python/english3e/…

therealjayvi Over a year ago

A thousand thanks! I appreciate the referral, I could really use all the help I can get; sometimes it feels like I'm trying to learn how to use a computer all over again. I genuinely appreciate the help.

GH05T Over a year ago

This might be an even better resource, but I haven't worked through it all yet: diveintopython3.net But, so far, I think it's fantastic, though maybe a little faster paced.

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