Python Replacing String with Class?

Question

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

• Bharel: Are they classes? If so you can pass them directly
• TerryA: Can you clarify on the 'types' A B C? Are they custom types?
• LOG: @TerryA like colors red green and blue. what are your suggestions?
• Anonymous12358: I think you're looking for enums.
• quamrana: Now we know what your types are, what is in the ...? How does that vary depending on item_type?

Answer 1

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

Answer 2

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

• LOG: Do I need 3 classes A,B,C? but all types are types of same object... they should be one
• LOG: See my comment please, I still believe no need for 3 classes. For example I mean Red, Green and Blue (all colors)
• Alexander: Do you need all 3? It depends on what you plan to use them for.
• Alexander: @log see the bottom of my answer... all three are not needed

Answer 3

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