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

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 <donbarbos@proton.me>

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.

And see also donbarbos#2.

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 <1324225+hugovk@users.noreply.github.com>

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

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

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 '
)

Thank you!

Big thanks!

…nt` (python#136964) Co-authored-by: stodoran <stefan.todoran@uipath.com> Co-authored-by: StefanTodoran <stefan.alex4@gmail.com> Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com> Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

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 <donbarbos@proton.me>

Update Doc/library/pprint.rst

cbc392d

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Update Doc/library/pprint.rst

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Update Doc/library/pprint.rst

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Update Doc/library/pprint.rst

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Update Doc/whatsnew/3.14.rst

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Update Lib/pprint.py

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Update Lib/pprint.py

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Update Lib/pprint.py

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Update Lib/pprint.py

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Update Lib/pprint.py

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Update Lib/pprint.py

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Update Lib/test/test_pprint.py

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Update Lib/test/test_pprint.py

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Update Lib/test/test_pprint.py

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donbarbos added 2 commits July 22, 2025 07:35

Merge branch 'main' into issue-112632

fa0329b

Move to new whatsnew entry

ed2fcda

hugovk mentioned this pull request Mar 24, 2026

pprint: Rename block_style to expand donbarbos/cpython#1

Merged

Rename block_style to expand (#1 )

af663a8

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 )

1ca9963

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

Apply suggestions from code review

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Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

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

b1df0bb

Implement expand=True for str

c3dfaab

Add trailing comma when expanded

8f48ddb

Update docs

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hugovk approved these changes Mar 29, 2026

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hugovk merged commit 132abfd into python:main Apr 7, 2026
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hugovk mentioned this pull request Apr 13, 2026

gh-134551: Add t-strings support to pprint #134577

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

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

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