Overriding <= and >= for Python Class

Question

I have following class:

class Word:
    def __init__(self, key: str):
        self.key = key
        self.value = ''.join(sorted(key))

    def __lt__(self, other):
        if self.value < other.value:
            return True
        return False

    def __gt__(self, other):
        if self.value > other.value:
            return True
        return False

    def __eq__(self, other):
        val = other.value
        if self.value == val:
            return True
        return False

and < works. But when I try <= I get following error:

TypeError: '<=' not supported between instances of 'Word' and 'Word'

How to override <= for python class?

You might want to use the decorator [`functools.total_ordering`](https://docs.python.org/3.8/library/functools.html#functools.total_ordering). — Matthias, Apr 14 '20 at 11:49

score 1 · Accepted Answer · answered Apr 14 '20 at 11:47

You need to implement __ge__ & __le__

class Word:
    def __init__(self, key: str):
        self.key = key
        self.value = ''.join(sorted(key))

    def __lt__(self, other):
        if self.value < other.value:
            return True
        return False

    def __gt__(self, other):
        if self.value > other.value:
            return True
        return False

    def __le__(self, other):
        if self.value <= other.value:
            return True
        return False

    def __ge__(self, other):
        if self.value >= other.value:
            return True
        return False

    def __eq__(self, other):
        val = other.value
        if self.value == val:
            return True
        return False

Patrick Artner · Answer 2 · 2020-04-14T11:55:35.750

You need to override def __le__(self, other) (lesser-equal) and def __ge__(self, other) (greater equal) as well.

Beside that you should check if your given other actually is a Word instance, else you might crash because no other.value can be accessed:

w = Word("hello")
print( w > 1234 )  # crash:  AttributeError: 'int' object has no attribute 'value'

Source / Documentation of all of them: object.__le__

See

python overloading operators

Potential fix for comparison:

def __lt__(self, other):
    if isinstance(other, Word):
        if self.value < other.value:
            return True
    else:
        # return True or False if it makes sense - else use better exception
        raise ValueError(f"Cannot compare Word vs. {type(other)}")
    return False

score 1 · Answer 3 · answered Apr 14 '20 at 12:32

1

There is another special method for this:

 def __le__(self, other):
    if self.value <= other.value:
        return True
    else:
        return False

answered Apr 14 '20 at 12:32

Usman Abasi

11
2

Overriding <= and >= for Python Class

3 Answers3