gh-112632: Add optional keyword-only argument `expand` to `pprint` by donbarbos · Pull Request #136964 · python/cpython

donbarbos · 2025-07-22T07:34:15Z

cc @tomasr8 as the previous reviewer (tests coverage problem fixed)

Issue: pprint with compact indent #112632

📚 Documentation preview 📚: https://cpython-previews--136964.org.readthedocs.build/

…esting that in the particular unit test)

Co-authored-by: donBarbos <[email protected]>

hugovk · 2026-03-24T22:32:03Z

Thanks for working on this, it's looking good!

Is "block style JSON formatting" an established term? Wondering if there's a better explanation. Maybe just "pretty-printed JSON" is better?

I've also opened donbarbos#1 to suggest renaming block_style to expand, as it mirrors compact well.

Black uses the word "explode", which I'm not sure fits here, but "expand" is similar.

And let's update from main after merging donbarbos#1, it's been a while since this ran CI.

hugovk

And see also donbarbos#2.

Doc/library/pprint.rst

Doc/whatsnew/3.15.rst

Lib/pprint.py

hugovk · 2026-03-27T13:42:54Z

Here's a visual test on a bunch of types:

script

import collections
import dataclasses
import pprint
import types

pp = lambda label, obj: print(
    f"--- {label} ---\n{pprint.pformat(obj, width=20, indent=4, expand=True)}\n"
)

pp("dict", {"foo": "bar", "baz": 123, "qux": [1, 2, 3], "quux": {"a": "b"}})

pp("list", ["foo", "bar", "baz", "qux", "quux"])

pp("tuple", ("foo", "bar", "baz", 4, 5, 6))

pp("tuple (single)", ("only",))

pp("set", {"foo", "bar", "baz", "qux", (1, 2, 3)})

pp("frozenset", frozenset({"foo", "bar", "baz", (1, 2, 3)}))

pp("OrderedDict", collections.OrderedDict([("foo", 1), ("bar", 12), ("baz", 123)]))

dd = collections.defaultdict(list)
dd["foo"].extend(["bar", "baz", "qux"])
dd["bar"] = {"a": "b", "c": None}
pp("defaultdict", dd)

pp("Counter", collections.Counter("abcdeabcdabcaba"))

pp("ChainMap", collections.ChainMap({"foo": "bar"}, {"baz": "qux"}, {"a": [1, 2, 3]}))

pp("deque", collections.deque(["foo", 123, {"a": "b"}, [1, 2, 3]]))

pp("deque (maxlen)", collections.deque(["foo", 123, {"a": "b"}], maxlen=10))


@dataclasses.dataclass
class Point:
    x: float
    y: float
    label: str
    tags: list = dataclasses.field(default_factory=list)


pp("dataclass", Point(1.0, 2.5, "origin", ["a", "b", "c"]))

pp(
    "SimpleNamespace",
    types.SimpleNamespace(foo="bar", count=42, nested=types.SimpleNamespace(x=1, y=2)),
)

pp("bytes", b"Hello world! foo bar baz 123 456 789")

pp("bytearray", bytearray(b"Hello world! foo bar baz 123 456 789"))

pp("mappingproxy", types.MappingProxyType({"foo": "bar", "baz": 123, "qux": [1, 2]}))

pp("frozendict", frozendict({"foo": "bar", "baz": 123, "qux": [1, 2]}))

pp("dict_keys", {"foo": 1, "bar": 2, "baz": 3, "qux": 4, "quux": 5}.keys())

pp("dict_values", {"foo": 1, "bar": 2, "baz": 3, "qux": 4, "quux": 5}.values())

pp("dict_items", {"foo": 1, "bar": 2, "baz": 3, "qux": 4, "quux": 5}.items())

pp("str", "The quick brown fox jumped over the lazy dog " * 3)

pp("UserDict", collections.UserDict({"foo": "bar", "baz": 123, "qux": [1, 2]}))

pp("UserList", collections.UserList(["foo", "bar", "baz", "qux", "quux"]))

pp(
    "UserString",
    collections.UserString("The quick brown fox jumped over the lazy dog " * 3),
)

The new frozendict, other dict_* and str need updating to support expand:

--- frozendict ---
frozendict({
               'baz': 123,
               'foo': 'bar',
               'qux': [
                   1,
                   2
               ]
           })

--- dict_keys ---
dict_keys([       'bar',
    'baz',
    'foo',
    'quux',
    'qux'])

--- dict_values ---
dict_values([       1,
    2,
    3,
    4,
    5])

--- dict_items ---
dict_items([       ('bar', 2),
    ('baz', 3),
    ('foo', 1),
    ('quux', 5),
    ('qux', 4)])

--- str ---
('The quick brown '
 'fox jumped over '
 'the lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog ')

Full output

--- dict ---
{
    'baz': 123,
    'foo': 'bar',
    'quux': {'a': 'b'},
    'qux': [1, 2, 3]
}

--- list ---
[
    'foo',
    'bar',
    'baz',
    'qux',
    'quux'
]

--- tuple ---
(
    'foo',
    'bar',
    'baz',
    4,
    5,
    6
)

--- tuple (single) ---
('only',)

--- set ---
{
    'bar',
    'baz',
    'foo',
    'qux',
    (1, 2, 3)
}

--- frozenset ---
frozenset({
    'bar',
    'baz',
    'foo',
    (1, 2, 3)
})

--- OrderedDict ---
OrderedDict([
    ('foo', 1),
    ('bar', 12),
    ('baz', 123)
])

--- defaultdict ---
defaultdict(<class 'list'>, {
    'bar': {
        'a': 'b',
        'c': None
    },
    'foo': [
        'bar',
        'baz',
        'qux'
    ]
})

--- Counter ---
Counter({
    'a': 5,
    'b': 4,
    'c': 3,
    'd': 2,
    'e': 1
})

--- ChainMap ---
ChainMap(
    {'foo': 'bar'},
    {'baz': 'qux'},
    {
        'a': [1, 2, 3]
    }
)

--- deque ---
deque([
    'foo',
    123,
    {'a': 'b'},
    [1, 2, 3]
])

--- deque (maxlen) ---
deque([
    'foo',
    123,
    {'a': 'b'}
], maxlen=10)

--- dataclass ---
Point(
    x=1.0,
    y=2.5,
    label='origin',
    tags=['a', 'b', 'c']
)

--- SimpleNamespace ---
namespace(
    foo='bar',
    count=42,
    nested=namespace(
        x=1,
        y=2
    )
)

--- bytes ---
(
    b'Hello world!'
    b' foo bar baz'
    b' 123 456 789'
)

--- bytearray ---
bytearray(
    b'Hello world!'
    b' foo bar baz'
    b' 123 456 789'
)

--- mappingproxy ---
mappingproxy({
    'baz': 123,
    'foo': 'bar',
    'qux': [1, 2]
})

--- frozendict ---
frozendict({
               'baz': 123,
               'foo': 'bar',
               'qux': [
                   1,
                   2
               ]
           })

--- dict_keys ---
dict_keys([       'bar',
    'baz',
    'foo',
    'quux',
    'qux'])

--- dict_values ---
dict_values([       1,
    2,
    3,
    4,
    5])

--- dict_items ---
dict_items([       ('bar', 2),
    ('baz', 3),
    ('foo', 1),
    ('quux', 5),
    ('qux', 4)])

--- str ---
('The quick brown '
 'fox jumped over '
 'the lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog ')

--- UserDict ---
{
    'baz': 123,
    'foo': 'bar',
    'qux': [1, 2]
}

--- UserList ---
[
    'foo',
    'bar',
    'baz',
    'qux',
    'quux'
]

--- UserString ---
('The quick brown '
 'fox jumped over '
 'the lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog ')

* Move recursive_indent calculation into helper * Move indent padding into helper

Co-authored-by: Hugo van Kemenade <[email protected]>

hugovk · 2026-03-28T10:59:11Z

Would you like to have a go at adding support for frozendict, dict_* and str or shall I have a look?

donbarbos · 2026-03-28T15:14:43Z

Would you like to have a go at adding support for frozendict, dict_* and str or shall I have a look?

I'd like to do it myself, but I don't think I'll be able to devote enough time to it in the near future. So I'd be grateful for help

hugovk · 2026-03-29T10:17:35Z

I've also added a trailing comma when expanded, similar to modern Black/Ruff style:

Full output

--- dict ---
{
 'baz': 123,
 'foo': 'bar',
 'quux': {'a': 'b'},
 'qux': [1, 2, 3],
}

--- list ---
[
 'foo',
 'bar',
 'baz',
 'qux',
 'quux',
]

--- tuple ---
(
 'foo',
 'bar',
 'baz',
 4,
 5,
 6,
)

--- tuple (single) ---
('only',)

--- set ---
{
 'bar',
 'baz',
 'foo',
 'qux',
 (1, 2, 3),
}

--- frozenset ---
frozenset({
 'bar',
 'baz',
 'foo',
 (1, 2, 3),
})

--- OrderedDict ---
OrderedDict([
 ('foo', 1),
 ('bar', 12),
 ('baz', 123),
])

--- defaultdict ---
defaultdict(<class 'list'>, {
 'bar': {
  'a': 'b',
  'c': None,
 },
 'foo': [
  'bar',
  'baz',
  'qux',
 ],
})

--- Counter ---
Counter({
 'a': 5,
 'b': 4,
 'c': 3,
 'd': 2,
 'e': 1,
})

--- ChainMap ---
ChainMap(
 {'foo': 'bar'},
 {'baz': 'qux'},
 {'a': [1, 2, 3]},
)

--- deque ---
deque([
 'foo',
 123,
 {'a': 'b'},
 [1, 2, 3],
])

--- deque (maxlen) ---
deque([
 'foo',
 123,
 {'a': 'b'},
], maxlen=10)

--- dataclass ---
Point(
 x=1.0,
 y=2.5,
 label='origin',
 tags=['a', 'b', 'c'],
)

--- SimpleNamespace ---
namespace(
 foo='bar',
 count=42,
 nested=namespace(x=1, y=2),
)

--- bytes ---
(
 b'Hello world! foo'
 b' bar baz 123 456'
 b' 789'
)

--- bytearray ---
bytearray(
 b'Hello world! foo'
 b' bar baz 123 456'
 b' 789'
)

--- mappingproxy ---
mappingproxy({
 'baz': 123,
 'foo': 'bar',
 'qux': [1, 2],
})

--- frozendict ---
frozendict({
 'baz': 123,
 'foo': 'bar',
 'qux': [1, 2],
})

--- dict_keys ---
dict_keys([
 'bar',
 'baz',
 'foo',
 'quux',
 'qux',
])

--- dict_values ---
dict_values([
 1,
 2,
 3,
 4,
 5,
])

--- dict_items ---
dict_items([
 ('bar', 2),
 ('baz', 3),
 ('foo', 1),
 ('quux', 5),
 ('qux', 4),
])

--- str ---
(
 'The quick brown '
 'fox jumped over '
 'the lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog '
)

--- UserDict ---
{
 'baz': 123,
 'foo': 'bar',
 'qux': [1, 2],
}

--- UserList ---
[
 'foo',
 'bar',
 'baz',
 'qux',
 'quux',
]

--- UserString ---
(
 'The quick brown '
 'fox jumped over '
 'the lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog The '
 'quick brown fox '
 'jumped over the '
 'lazy dog '
)

stodoran and others added 30 commits January 24, 2025 18:19

Added an option for block formatting to pprint

b9baf94

Small bug fix for indent=1, added to unit test

f5fcbfc

Merge branch 'main' into fix-issue-112632

31a4d1e

Remove set from block style unit test (since order kept changing)

a92ef3d

📜🤖 Added by blurb_it.

d9a147f

Merge branch 'main' into fix-issue-112632

ffef3b0

Fix params in news entry

19e4e08

Fix line length for news entry

8ef085f

Shorten news entry

c446aa1

Merge branch 'main' into fix-issue-112632

f9bd6ef

Address documentation related PR comments

49b1108

Merge branch 'main' into fix-issue-112632

62dd5e5

Fix length of title underline :/

0b8fd2b

Fix test case, remove unnecessary recursion on dataclass (we aren't t…

5f08960

…esting that in the particular unit test)

Merge branch 'main' into fix-issue-112632

ac71fc4

Update Doc/library/pprint.rst

59ed5fd

Co-authored-by: donBarbos <[email protected]>

Update Doc/library/pprint.rst

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pprint with compact indent #112632

Open

donbarbos added 2 commits July 22, 2025 07:35

Merge branch 'main' into issue-112632

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Move to new whatsnew entry

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hugovk mentioned this pull request Mar 24, 2026

pprint: Rename block_style to expand donbarbos/cpython#1

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Rename block_style to expand (#1)

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donbarbos requested a review from AA-Turner as a code owner March 25, 2026 18:43

Merge branch 'main' into issue-112632

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hugovk changed the title ~~gh-112632: Add optional keyword-only argument block_style to pprint~~ gh-112632: Add optional keyword-only argument expand to pprint Mar 25, 2026

hugovk reviewed Mar 27, 2026

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hugovk and others added 2 commits March 27, 2026 14:37

Move calculations into helpers (#2)

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* Move recursive_indent calculation into helper * Move indent padding into helper

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Co-authored-by: Hugo van Kemenade <[email protected]>

hugovk mentioned this pull request Mar 28, 2026

gh-112632 : Added an option for block formatting to pprint #129274

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hugovk added 4 commits March 28, 2026 21:13

Implement expand=True for frozendict

64238cd

Implement expand=True for dict views

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Implement expand=True for str

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Add trailing comma when expanded

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Update docs

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gh-112632: Add optional keyword-only argument `expand` to `pprint`#136964

gh-112632: Add optional keyword-only argument `expand` to `pprint`#136964
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