__lt__ instead of __cmp__

👻 Check our latest review to choose the best laptop for Machine Learning engineers and Deep learning tasks!

Python 2.x has two ways to overload comparison operators, __cmp__ or the "rich comparison operators" such as __lt__. The rich comparison overloads are said to be preferred, but why is this so?

Rich comparison operators are simpler to implement each, but you must implement several of them with nearly identical logic. However, if you can use the builtin cmp and tuple ordering, then __cmp__ gets quite simple and fulfills all the comparisons:

class A(object):
  def __init__(self, name, age, other):
    self.name = name
    self.age = age
    self.other = other
  def __cmp__(self, other):
    assert isinstance(other, A) # assumption for this example
    return cmp((self.name, self.age, self.other),
               (other.name, other.age, other.other))

This simplicity seems to meet my needs much better than overloading all 6(!) of the rich comparisons. (However, you can get it down to "just" 4 if you rely on the "swapped argument"/reflected behavior, but that results in a net increase of complication, in my humble opinion.)

Are there any unforeseen pitfalls I need to be made aware of if I only overload __cmp__?

I understand the <, <=, ==, etc. operators can be overloaded for other purposes, and can return any object they like. I am not asking about the merits of that approach, but only about differences when using these operators for comparisons in the same sense that they mean for numbers.

Update: As Christopher pointed out, cmp is disappearing in 3.x. Are there any alternatives that make implementing comparisons as easy as the above __cmp__?

👻 Read also: what is the best laptop for engineering students?

__lt__ instead of __cmp__ __del__: Questions

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

from time import sleep
sleep(0.1) # Time in seconds

__lt__ instead of __cmp__ __del__: Questions

We hope this article has helped you to resolve the problem. Apart from __lt__ instead of __cmp__, check other __del__-related topics.

Want to excel in Python? See our review of the best Python online courses 2023. If you are interested in Data Science, check also how to learn programming in R.

By the way, this material is also available in other languages:

• Italiano __lt__ instead of __cmp__
• Deutsch __lt__ instead of __cmp__
• Français __lt__ instead of __cmp__
• Español __lt__ instead of __cmp__
• Türk __lt__ instead of __cmp__
• Русский __lt__ instead of __cmp__
• Português __lt__ instead of __cmp__
• Polski __lt__ instead of __cmp__
• Nederlandse __lt__ instead of __cmp__
• 中文 __lt__ instead of __cmp__
• 한국어 __lt__ instead of __cmp__
• 日本語 __lt__ instead of __cmp__
• हिन्दी __lt__ instead of __cmp__