comparative.py

import operator
import logging

COMPARISONS = ("__lt__", "__le__", "__eq__", "__ne__", "__ge__", "__gt__")
logging.basicConfig(level=logging.INFO)
LOGGER = logging.getLogger(__name__)


def comparison_factory(op_name, strict, *attrs):
        comparable_attrs = operator.attrgetter(*attrs)

        def comparison(self, other):
            if strict and not isinstance(other, type(self)):
                return NotImplemented
            op_fn = getattr(operator, op_name)
            return op_fn(comparable_attrs(self), comparable_attrs(other))
        return comparison


def compare_by(*attrs, strict=True):
    if not attrs:
        raise TypeError("no attribute supplied")
    def decorator(cls):
        for op_name in COMPARISONS:
            op_fn = comparison_factory(op_name, strict, *attrs)
            setattr(cls, op_name, op_fn)
        return cls
    return decorator


if __name__ == "__main__":
    @compare_by("hour", "minute")
    class Clock:

        def __init__(self, hour=0, minute=0):
            self.hour = hour
            self.minute = minute

        def __str__(self):
            return "{0.hour:02d}:{0.minute:02d}".format(self)

        def __repr__(self):
            return "Clock(h={0.hour:}, m={0.minute:02d})".format(self)

    clock1 = Clock(12, 0)
    clock2 = Clock(12, 1)
    print("clock1 < clock2", clock1 < clock2)
    print("clock1 <= clock2", clock1 <= clock2)
    print("clock1 != clock2", clock1 != clock2)