How do I have a Python 3 program check if changing a variable's type would cause a crash before trying to change the type?

Question

I’m making a custom subroutine called userinput() in order to replace input().

I haven’t tried anything as I have no clue what to try.
The program crashes when I try to convert the input from a string to an int/float if the input is not a number.

Here’s the function:

def userinput(text,valan,valtype):
    if valan == 0 and valtype == 0:
        a = input(text)
    elif valan == 0 and valtype != 0:
        val = 0
        while val == 0:
            a = input(text)
            if valtype == "int":
                a = int(a)
            elif valtype == "float":
                a = float(a)
            if type(a) != valtype:
                print("Invalid answer.")
                time.sleep(1)
                print("Try again.")
                time.sleep(1)
            else:
                val = 1
    elif valan != 0 and valtype == 0:
        val = 0
        while val == 0:
            a = input(text)
            for i in range(0,len(valan)):
                if valan[i] == a:
                    val = 1
            if val == 0:
                print("Invalid answer.")
                time.sleep(1)
                print("Try again.")
                time.sleep(1)
    return a

Asked By: Nugget Gamer

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Source

Answer 1

I am not sure i understood correctly what you are trying to archieve with your function but you can try to catch the exception (ValueError) that python throws when trying to cast your variable to a different datatype.

The problem here might be those instructions like a = int(a) or a = float(a). You may try to replace them with:

try:
    a = int(a)
except ValueError:
    print("Int conversion Failed")

and

try:
    a = float(a)
except ValueError:
    print("Float conversion Failed")

Apart from that, it is not clear in your code for example if the valtype parameter should be an integer or a string (this may cause other errors). If you can give a more detailed explanation of your problem, maybe it’s easier also for other people to get in touch with you for helping.

Try/Catch documentation for further reading.

Answered By: Paolo

How do I have a Python 3 program check if changing a variable's type would cause a crash before trying to change the type?

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