Python Replacing String with Class?-CodePudding

I'm new to python so I don't really know a lot in this topic.

I have a function which gets item type, I have three types: A, B and C.

My initial approach was to pass item type as string, for example:

def my_function (item_type):
    if item_type == 'A': ...

But this is a bad approach, what are the alternatives? maybe class, but how to pass it to function

CodePudding user response：

Rather than working with strings, use enums. For example:

from enum import Enum

class Colour(Enum):
    RED = 0
    GREEN = 1
    BLUE = 2

If the colours need to be distinct then just make sure that the values assigned are all different.

Then you might have a function like this:

def func(colour):
    match colour:
        case Colour.RED:
            pass
        case Colour.GREEN:
            pass
        case Colour.BLUE:
            pass

Of course, the enum might be wrapped in some other class but this should get you started

CodePudding user response：

If you are checking instances of classes then you can use isinstance or check using the type function

class A:
   pass

a = A()
print(isinstance(a,A))  # this is the preferred method
print(type(a) == A)

OUTPUT

True
True

If you are checking the classes themselves then you can do a straight comparison.

class A:
    pass

print(A == A)

OUTPUT

True

If you are checking subclasses then you can use issubclass function

class Parent:
    pass

class A(Parent):
    pass

class B(Parent):
    pass

print(issubclass(A, Parent))
print(issubclass(B, Parent))

OUTPUT

True
True

Update from the question in your comment if you want to consolidate classes you could do something like this:

class Color:
    def __init__(self, color):
        self.color = color

red = Color('red')
blue = Color('blue')
green = Color('green')

print(red.color)
print(blue.color)
print(green.color)
print(isinstance(red, Color))
print(isinstance(green, Color))

OUTPUT

'red'
'blue'
'green'
True
True

CodePudding user response：

The good design usually avoids using isinstance() or type() calls. If you need some class-specific logic you better encapsulate it in a class itself. Please refer to: https://refactoring.guru/replace-conditional-with-polymorphism