CODEWITHSUNDEEP
pythonpython-3.x
Cedric H.
Cedric H.

Reputation: 8288

Python enum like construction with metaclass

For some reason, on a Sunday morning I felt like I needed the following for a scientific library I'm writing:

class PolarityType(type):
    """Metaclass to construct polarity types. Supports conversion to float and int."""
    def __float__(cls):
        return int(cls)

    def __int__(cls):
        return cls.P


class Polarity(metaclass=PolarityType):
    """Base class to build polarity."""
    P = 0


class PositivePolarity(Polarity):
    """Positive polarity."""
    P = 1


class NegativePolarity(Polarity):
    """Negative polarity."""
    P = -1

>>> float(NegativePolarity)
>>> -1.0

Basically instead of passing arguments like polarity='POSITIVE' and checking strings, and also because I'm using type hints, I wanted it to be strongly typed and I wrote the above code.

Does it make sense, is there a much easier/cleaner/better way to achieve the same result?

Upvotes: 1

Views: 361

Answers (1)

escaped
escaped

Reputation: 744

Your solution works, but is there a special reason not to use an enum?

import enum

class Polarity(enum.Enum):
    POSITIVE: float = 1.0
    NEGATIVE: float = -1.0

    def __float__(cls):
        return self.value

    def __int__(cls):
        return int(self.value)

print(Polarity.NEGATIVE, type(Polarity.NEGATIVE))
# Polarity.NEGATIVE <enum 'Polarity'>

print(type(Polarity.NEGATIVE.value), Polarity.NEGATIVE.value)
# <class 'float'> -1.0

print(type(float(Polarity.NEGATIVE)), float(Polarity.NEGATIVE))
# <class 'float'> -1.0

Upvotes: 4

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