max() fails in python2 -> python3 conversion with `>` not supported

Question

While converting from python 2.x -> python 3.x, I found this change in the behavior of the built-in max function. I didn't find it documented in any of the standard locations for migration issues. https://eev.ee/blog/2016/07/31/python-faq-how-do-i-port-to-python-3/ http://python-future.org/compatible_idioms.html

How do I fix this?

Python 2.x:

In [1]: max([None, None, None])
In [2]:

Python 3.x:

In [3]: max([None, None, None])
---------------------------------------------------------------------------
TypeError                                
Traceback (most recent call last) <ipython-input-3-f82c85b9875c> in <module>()
----> 1 max([None, None, None])

TypeError: '>' not supported between instances of 'NoneType' and 'NoneType'

https://docs.python.org/3.0/whatsnew/3.0.html#ordering-comparisons — Michael Butscher, Dec 03 '17 at 03:32
I'm voting to close this question as off-topic because it is not a question. — jwodder, Dec 03 '17 at 03:32
I answered my own "question" (see below), which is supposed to be explicitly encouraged in order to help others. — Shankari, Dec 03 '17 at 03:39
@Shankari: Yes, answering your own question is allowed, but I still don't see anything that looks like a question in the "question" part of this post. — jwodder, Dec 03 '17 at 03:40
You may find [this](https://stackoverflow.com/q/26575183/7207392) interesting. — Paul Panzer, Dec 03 '17 at 03:45
I can change the question to be "I got this error, it is not listed in the FAQs, what do I do?". It seems a bit lame to me, but I can do it if it makes people happier. — Shankari, Dec 03 '17 at 03:46
@jwodder If it is not a question, how can it have an answer? ;-) — Paul Panzer, Dec 03 '17 at 03:50
@Shankari Formulate the question in a way as it probably would be entered here or in Google by someone to find an answer. — Michael Butscher, Dec 03 '17 at 03:51

Shankari · Accepted Answer · 2017-12-04T06:22:57.107

Answering my own question: there is no backwards compatible max, but it is arguable that trying to find the max of None doesn't really make sense.

The entries that I was comparing were timestamps, and I knew that they would never be negative. So I changed my code to return 0 instead of None, so the max turned to max([0,0,0]) which worked.

If you can't make such guarantees about your data, you could return -sys.maxsize instead.

In [7]: max([-sys.maxsize, -sys.maxsize, -sys.maxsize])
Out[7]: -9223372036854775807

Note sys.maxsize not sys.maxint, which is a documented change. What is sys.maxint in Python 3?

score -1 · Answer 2 · answered Dec 03 '17 at 07:24

-1

None represent the absence of a value in Python3 shows the error message ,because you dont search the largest item in arguments list of type NoneType

answered Dec 03 '17 at 07:24

José Carlos Aquino

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max() fails in python2 -> python3 conversion with `>` not supported

2 Answers2