Teach pprint about dict views

[rhettinger]

BPO	45959
Nosy	@rhettinger, @devdanzin, @merwok, @AlexWaygood, @david-peled, @joshinsel
PRs	gh-90117: handle dict and mapping views in pprint #30135

^{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 2021-12-02.07:06:56.201>
labels = ['easy', 'type-feature', 'library', '3.11']
title = 'Teach pprint about dict views'
updated_at = <Date 2022-01-18.01:57:55.609>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2022-01-18.01:57:55.609>
actor = 'eric.araujo'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-12-02.07:06:56.201>
creator = 'rhettinger'
dependencies = []
files = []
hgrepos = []
issue_num = 45959
keywords = ['patch', 'easy']
message_count = 5.0
messages = ['407513', '408582', '408648', '408682', '410839']
nosy_count = 6.0
nosy_names = ['rhettinger', 'ajaksu2', 'eric.araujo', 'AlexWaygood', 'david-peled', 'joshinsel']
pr_nums = ['30135']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45959'
versions = ['Python 3.11']

Linked PRs

• GH-90117: Check for list and tuple before MappingView in pprint #135779

[rhettinger]

The pprint() code has a number of type or protocol specific handlers but doesn't have one for dict views. So, we don't get pretty printing for the key(), values(), and items():

d = {i:i for i in range(100)}
pprint(d)             # This is handled correctly
pprint(d.keys())      # Printed on one line
pprint(d.values())    # Printed on one line
pprint(d.items())     # Printed on one line

[joshinsel]

According to the documentation for pprint, it is supposed to print objects on a single line if possible. See the second paragraph here: https://docs.python.org/3/library/pprint.html

[rhettinger]

More accurate to say that it aspires to print in a single line ONLY if the content fits in the specified width. Otherwise, it prints vertically with appropriate indentation. Indeed, that is the entire purpose of the module; otherwise, we would just use print() which always writes one line.

[devdanzin]

I have tried to add this. The PR adds:

• PrettyPrinter._pprint_dict_view to handle dict_keys and dict_values (sorted with _safe_key).
  = PrettyPrinter._pprint_dict_items_view to handle dict_items (sorted using _safe_tuple).
• Tests.

Would a NEWS entry or other form of documentation be necessary?

[merwok]

The PR looks good! When the last comments are resolved, unless there is activity from other core devs, I will merge it.

[AbhigyanBose]

@merwok Hey, what's the situation with the PR for this issue ?

Is there anything that needs to be done in the PR ?
If there is, I'm happy to help complete it, or put in a different PR, whichever is required.