Type check of user input and exclude negative numbers with exceptions

Question

I have the following method, which I use to take inputs from the user and handle it via exceptions until they fullfill the criteria.

    def enter_data(self, message: str, typ: type):
        while True:
            try:
                v = typ(input(message))
                if isinstance(v, int) or isinstance(v, float) and v < 0:
                    raise ValueError
            except ValueError:
                print(f"Thats not an {typ}! or you have entered a negative")
                continue
            else:
                break
        return v

This is the way I call it

 def add_item_interaction(self) -> None:
   add_item_num = self.enter_data("What is the new items #?n", int)
   add_item_price = self.enter_data("What is the new items price?n", float)
   add_item_quant = self.enter_data("What is the new items quantity?n", int)
   add_name = self.enter_data("What is the new items name?n", str)

This doesn’t seem to work for any type entered, no matter if it is a negative or matches what I specify.

Any Help Here? I know I must be close.

For example:

When I run add_item_num = self.enter_data("What is the new items #?n", int), and input 1, I get: "Thats not an int!", even though the input is an int, and positive, so it should not trigger the if isinstance(...) statement

Asked By: py_coder1019

||

Source

Answer 1

This boils down to a True or False and False = True problem.
Without paranthesis this is executed like this

or(True, and(False,False))

The first value is instantly returned and the others are not evaluated.

Your idea is perfect you just need to add the parantheses

   def enter_data(self, message: str, typ: type):
        while True:
            try:
                v = typ(input(message))
                if (isinstance(v, int) or isinstance(v, float)) and v < 0:
                    raise ValueError
            except ValueError:
                print(f"Thats not an {typ}! or you have entered a negative")
                continue
            else:
                break
        return v

Answered By: Daraan

Type check of user input and exclude negative numbers with exceptions

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