Not wanting to use if else but try except block in python

Question

I am trying to write a program that does the following in python:

accept three arguments: a prompt, a low acceptable limit, and a high acceptable limit;
if the user enters a string that is not an integer value, the function should emit the message Error: wrong input, and ask the user to input the value again;
if the user enters a number which falls outside the specified range, the function should emit the message Error: the value is not within permitted range (min..max) and ask the user to input the value again;
if the input value is valid, return it as a result.

I don’t want to use if-else. I am learning catching exceptions in python. i want to use try-except

I have written the following code

def readint(prompt, min, max):
    try:
        theNum = int(input(prompt))
        if theNum in range(min, max+1):
            return theNum
    except ValueError: 
            return "Error: wrong input. The value is not within the permitted range (-10..10)"
            readint(prompt, min, max)
       
v = readint("Enter a number from -10 to 10: ", -10, 10)

print("The number is:", v)

The output prints out any number in the mentioned range but when a number not within the range is entered, the output says "The number is: None" and it does not re-prompt me to enter another number

Asked By: binbbaz

||

Source

Answer 1

Here’s a typical retry loop that uses try/except:

def thing_to_retry():
    while True:
        try:
            return thing()
        except SomeError as e:
            print("Whoopsie! Error: {}".format(e))

Since the try/except is within the loop, any exception you catch will cause another loop iteration. Success will cause the function to return from the loop.

Answered By: Tom

Answer 2

min and max are keywords in python. I would avoid using them as variable names.

def readint(prompt, minimum, maximum):
    while True:
        try:
            value = int(input(prompt))
            assert minimum <= value <= maximum
            prompt = "Try again: "
        except ValueError:
            print("Error: Not an integer")
        except AssertionError:
            print("Error: Value not within range")
        else:
            break
    return value

minimum = -10
maximum = 10

value = readint(f"Enter a number between {minimum} and {maximum}: ", minimum, maximum)

Answered By: Paul M.

Answer 3

def readint(prompt, min, max):
    doIt = True
    while doIt:
    
        try:
            userInput = int(input(prompt))
            if userInput in range(min, max+1):
                doIt = False
                return userInput
            else:
                raise AssertionError
        except ValueError:
            print("Error: wrong input.")
        except AssertionError:
            print("The value is not within the permitted range (-10..10)") 
        except:
            doIt = True
        
v = readint("Enter a number from -10 to 10: ", -10, 10)

print("The number is:", v)

Answered By: Adil_Sheraz

Answer 4

def read_int(prompt, min, max):
    #
    while True:
        try:
            value = int(input(prompt))
            assert min <= value <= max
            return value

        except AssertionError:
            print("Error: the value is not within permitted range (-10..10)")

        except ValueError:
            print("Error: wrong input")

        else:
            break

    #
v = read_int("Enter a number from -10 to 10: ", -10, 10)

print("The number is:", v)

Answered By: Isaac Sackitey

Answer 5

The problem with None is that you do not write: return readint(prompt, min, max)
You just write readint(prompt, min, max)
If you like recursion ( I don’t) instead of a loop then you may try this:

def readint(prompt, mini, maxi):    
    try:
        theNum = int(input(prompt))
        assert theNum in range(mini, maxi + 1)
        return theNum
    except AssertionError:
        print("Error: wrong input. The value is not within the permitted range (-10..10)")       
    except ValueError:
        print("This is not a number")
    return readint(prompt, mini, maxi)

Answered By: manoliar

Not wanting to use if else but try except block in python

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