Receiving errors when defining functions (no self parameter, and invalid var type)-CodePudding

I'm trying to make a Python module which provides functions for user input. My code looks like this:

class PyInput:
    def inputString(prompt = "Enter a string: >>> "):
        """inputString asks the user to input a string."""

        userInput = input(prompt)
        str(userInput)
        return userInput

Unfortunately, I am getting multiple errors: The first says that "Instance methods should take a "self" parameter" (I know what this means, but is there a way to not have to define a function within a class to accept a "self" parameter?)

My second error is in my testing code, which looks like this:

from PyIO import *

vartest = "mystring"
tester = PyInput.inputString(vartest)
print(tester)

and it says that:

Argument of type "Literal['Input test: >>> ']" cannot be assigned to parameter "prompt" of type "PyInput" in function "inputString"
  "Literal['Input test: >>> ']" is incompatible with "PyInput"

I noticed that when I add "# type: ignore" to the lines that cause errors, my testing program runs as expected. Is there any way to fix this?

I'm using Python 3.11 on a Windows 11 64 bit laptop.

CodePudding user response：

To fix the first error, you need to add the self parameter to the method definition of inputString. This is because in Python, all instance methods (methods defined within a class) must accept a self parameter as their first argument. This parameter is used to refer to the instance of the object on which the method is being called.

Here's how you can update the inputString method to include the self parameter:

class PyInput:
    def inputString(self, prompt = "Enter a string: >>> "):
        """inputString asks the user to input a string."""

        userInput = input(prompt)
        str(userInput)
        return userInput

To fix the second error, you need to pass an instance of the PyInput class to the inputString method, instead of passing the string "mystring" as an argument. Here's how you can update your testing code to do this:

from PyIO import *

# Create an instance of the PyInput class
inputter = PyInput()

# Call the inputString method on the inputter instance, passing in the desired prompt as an argument
vartest = inputter.inputString("Input test: >>> ")

print(vartest)

And here's your updated code:

class PyInput:
    def inputString(self, prompt = "Enter a string: >>> "):
        """inputString asks the user to input a string."""

        userInput = input(prompt)
        str(userInput)
        return userInput

from PyIO import *

# Create an instance of the PyInput class
inputter = PyInput()

# Call the inputString method on the inputter instance, passing in the desired prompt as an argument
vartest = inputter.inputString("Input test: >>> ")

print(vartest)

CodePudding user response：

Actually, there is a way to define functions inside a class without the self parameter if you decorate it using @staticmethod. For example:

class Example:

    @staticmethod
    def answer():
        print('42')

The other answer by @torres9992 sufficiently answers your second question.