pprint does not keep the order of dict keys

[mattermat]

Bug report

Bug description:

As in the title:

from pprint import pprint

a = {
    "a": [1, 2, 3],
    "b": [1, 2, 3],
    "c": [1, 2, 3],
}

b = {
    "b": [1, 2, 3],
    "c": [1, 2, 3],
    "a": [1, 2, 3],
}

pprint(a)
pprint(b)

gives the following:

{'a': [1, 2, 3], 'b': [1, 2, 3], 'c': [1, 2, 3]}
{'a': [1, 2, 3], 'b': [1, 2, 3], 'c': [1, 2, 3]}

CPython versions tested on:

3.12

Operating systems tested on:

Windows

[kotnen]

This is the expected behaviour, and is not a bug.

From the documentation,

If sort_dicts is true (the default), dictionaries will be formatted with their keys sorted, otherwise they will display in insertion order.

As a side note, it's always good to check the documentation to see what the expected behaviour is before reporting something as a bug. (Please don't take that as a criticism of this bug report though; it's appreciated that you took the time out of your day to help out the Python project.)

[AlexWaygood]

Thanks for the report! As @kotnen says, this is longstanding and intentional behaviour that we wouldn't be able to easily change without breaking backwards compatibility. However, I think there's a number of documentation improvements we could make here to call out the default behaviour of pprint.pprint() so that users are more aware of it. I've opened #115986 to track that.

[mattermat]

Hi @kotnen ,

I should have checked the documentation before opening the issue...
Given that dict keeps the order of the keys I didn't expect pprint not doing the same.

Thanks for you feedback!

[terryjreedy]

pprint predate ordered keys by at least a decade. Sorting keys was then part of the expectation of 'pretty'. It also enabled a predictable output string for doctests.