__lt__ instead of __cmp__

| | | | | | |

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__?

__lt__ instead of __cmp__ __del__: Questions

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.


Answer #1

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

Here is another example where something is run approximately once a minute:

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


Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

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

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?


Answer #1

Path objects from the Python 3.4+ pathlib module also expose these instance methods:

__lt__ instead of __cmp__ cmp: Questions


Best laptop for Fortnite


Best laptop for Excel


Best laptop for Solidworks


Best laptop for Roblox


Best computer for crypto mining


Best laptop for Sims 4


Best laptop for Zoom


Best laptop for Minecraft


Latest questions


psycopg2: insert multiple rows with one query

12 answers


How to convert Nonetype to int or string?

12 answers


How to specify multiple return types using type-hints

12 answers


Javascript Error: IPython is not defined in JupyterLab

12 answers



Python OpenCV | cv2.putText () method

numpy.arctan2 () in Python

Python | os.path.realpath () method

Python OpenCV | cv2.circle () method

Python OpenCV cv2.cvtColor () method

Python - Move item to the end of the list

time.perf_counter () function in Python

Check if one list is a subset of another in Python

Python os.path.join () method