Python classes __le__() method

The __le__() method implements the internal workings of the less than or equal to operator ( <=) . When we use the <= operator as in x <= y, Python internally calls the __le__() method on object x with y as the argument, i.e x.__le__(y). 

Most builtin data types have this method implemented. This makes it possible to use the <= operator on various data type objects.

print(int(10).__le__(20)) # same as print(10 <= 20)

print("abc".__le__("xyz"))#Same as print("abs" <= "xyz")

print([5, 4, 3].__le__([1, 2, 3]))#Same as print([5, 4, 3] <= [1, 2, 3])

In most cases, the method is used  primarily with objects belonging to the same class/type. Either the TypeError or the NotImplemented exception may be raised if we use the method with objects from different classes.

print(int(10).__le__("10"))

Implementing the __le__() method for custom objects

In order to be able to use the <= operator on user-defined objects, the involved objects must implement the __le__() method based on their internal logic.

class MyClass:
    def __le__(self, other):
        #Statements

#A class for heights in meters
class Height:
     def __init__(self, value):
           self.value = value

     #define the __le__() method
     def __le__(self, other):
        if isinstance(other, Height):
            #Check that the 'other' object is an instance of this class
            return self.value <= other.value
        #Raise an error if 'other' is not an instance of this class
        raise TypeError("Both objects should be instances of 'Height'")

h1 = Height(5.4)
h2 = Height(7.5)
h3 = Height(3.0)

print(h1 <= h2)
print(h2 <= h3)