max function reports type errors in incorrect order

[nkobald]

BPO	42563
Nosy	@ericvsmith, @serhiy-storchaka

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-12-04.00:57:36.757>
labels = ['type-bug', '3.8']
title = 'max function reports type errors in incorrect order'
updated_at = <Date 2020-12-04.16:18:21.358>
user = 'https://bugs.python.org/nkobald'

bugs.python.org fields:

activity = <Date 2020-12-04.16:18:21.358>
actor = 'eric.smith'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2020-12-04.00:57:36.757>
creator = 'nkobald'
dependencies = []
files = []
hgrepos = []
issue_num = 42563
keywords = []
message_count = 3.0
messages = ['382463', '382469', '382501']
nosy_count = 3.0
nosy_names = ['eric.smith', 'serhiy.storchaka', 'nkobald']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42563'
versions = ['Python 3.8']

[nkobald]

I'm not _sure_ this is a bug, but I thought the behaviour was a bit odd. If you run max with a str and an int in different orders, you get this behaviour:

>>> max(123, 'hello')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '>' not supported between instances of 'str' and 'int'
>>> max(123, 'hello')

>>> max('hello', 123)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '>' not supported between instances of 'int' and 'str'

Note that order of the error message: 'int' and 'str' is the inverse of the order the str and int really are.

Did a search for max and didn't find this.

[serhiy-storchaka]

This is because the code of the main() function is roughly equivalent to

    result = next(iter)
    for item in iter:
        if item > result:
            result = item

It can be changed to use "result < item" instead of "item > result", but it can has subtle differences in behavior. I am not sure what is better.

If we change it, it can only be in 3.10, because of the risk of affecting user code.

[ericvsmith]

I don't think making a change would be worth the risk.

[iritkatriel]

From the discussion I think we're not going to change this. Marking as pending and will close soon if there will be no objections.