gh-91114: Added argument for json dump/dumps to print arrays (from lists and tuples) on one line

Doc/library/json.rst

@@ -239,6 +239,12 @@ Basic Usage
    .. versionchanged:: 3.6
       All optional parameters are now :ref:`keyword-only <keyword-only_parameter>`.
 
+   :param bool arr_oneline:
+      **New in this release.**
+      If ``True``, JSON arrays (Python lists and tuples) will be serialized
+      on a single line regardless of the specified *indent* level. This allows
+      for a more compact representation of array data while still pretty-printing
+      objects.  Default is ``False``.
 
 .. function:: dumps(obj, *, skipkeys=False, ensure_ascii=True, \
                     check_circular=True, allow_nan=True, cls=None, \
@@ -450,8 +456,7 @@ Encoders and Decoders
       This can be used to decode a JSON document from a string that may have
       extraneous data at the end.
 
-
-.. class:: JSONEncoder(*, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None)
+.. class:: JSONEncoder(*, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None, arr_oneline=False)
 
    Extensible JSON encoder for Python data structures.
 
@@ -518,19 +523,26 @@ Encoders and Decoders
    .. versionchanged:: 3.2
       Allow strings for *indent* in addition to integers.
 
-   If specified, *separators* should be an ``(item_separator, key_separator)``
-   tuple.  The default is ``(', ', ': ')`` if *indent* is ``None`` and
-   ``(',', ': ')`` otherwise.  To get the most compact JSON representation,
+   If specified, *separators* should be a ``(item_separator, key_separator)``
+   tuple.  The default is ``(', ', ': ')`` if *indent* is ``None``
+   and ``(',', ': ')`` otherwise.  To get the most compact JSON representation,
    you should specify ``(',', ':')`` to eliminate whitespace.
 
    .. versionchanged:: 3.4
       Use ``(',', ': ')`` as default if *indent* is not ``None``.
-
+   
    If specified, *default* should be a function that gets called for objects that
    can't otherwise be serialized.  It should return a JSON encodable version of
    the object or raise a :exc:`TypeError`.  If not specified, :exc:`TypeError`
    is raised.
-
+
+   :param bool arr_oneline:
+      **New in this release.**
+      When ``True``, JSON arrays (lists and tuples) are rendered on a single line,
+      even if an *indent* level is specified. This option allows for a more compact
+      representation of array data while still enabling pretty-printing of objects.
+      Default is ``False``.
+
    .. versionchanged:: 3.6
       All parameters are now :ref:`keyword-only <keyword-only_parameter>`.
 
@@ -828,4 +840,4 @@ Command-line options
    <https://www.rfc-editor.org/errata_search.php?rfc=7159>`_,
    JSON permits literal U+2028 (LINE SEPARATOR) and
    U+2029 (PARAGRAPH SEPARATOR) characters in strings, whereas JavaScript
-   (as of ECMAScript Edition 5.1) does not.
+   (as of ECMAScript Edition 5.1) does not.

Lib/json/__init__.py

@@ -119,7 +119,7 @@
 
 def dump(obj, fp, *, skipkeys=False, ensure_ascii=True, check_circular=True,
         allow_nan=True, cls=None, indent=None, separators=None,
-        default=None, sort_keys=False, **kw):
+        default=None, sort_keys=False, arr_oneline=False, **kw):
     """Serialize ``obj`` as a JSON formatted stream to ``fp`` (a
     ``.write()``-supporting file-like object).
 
@@ -155,6 +155,8 @@ def dump(obj, fp, *, skipkeys=False, ensure_ascii=True, check_circular=True,
 
     If *sort_keys* is true (default: ``False``), then the output of
     dictionaries will be sorted by key.
+    If *arr_oneline* is true (default: ``False``), then lists/tuples will be
+    encoded as arrays on a single line.
 
     To use a custom ``JSONEncoder`` subclass (e.g. one that overrides the
     ``.default()`` method to serialize additional types), specify it with
@@ -172,8 +174,8 @@ def dump(obj, fp, *, skipkeys=False, ensure_ascii=True, check_circular=True,
             cls = JSONEncoder
         iterable = cls(skipkeys=skipkeys, ensure_ascii=ensure_ascii,
             check_circular=check_circular, allow_nan=allow_nan, indent=indent,
-            separators=separators,
-            default=default, sort_keys=sort_keys, **kw).iterencode(obj)
+            separators=separators, default=default, sort_keys=sort_keys,
+            arr_oneline=arr_oneline, **kw).iterencode(obj)
     # could accelerate with writelines in some versions of Python, at
     # a debuggability cost
     for chunk in iterable:
@@ -182,7 +184,7 @@ def dump(obj, fp, *, skipkeys=False, ensure_ascii=True, check_circular=True,
 
 def dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True,
         allow_nan=True, cls=None, indent=None, separators=None,
-        default=None, sort_keys=False, **kw):
+        default=None, sort_keys=False, arr_oneline=False, **kw):
     """Serialize ``obj`` to a JSON formatted ``str``.
 
     If ``skipkeys`` is true then ``dict`` keys that are not basic types
@@ -217,6 +219,8 @@ def dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True,
 
     If *sort_keys* is true (default: ``False``), then the output of
     dictionaries will be sorted by key.
+    If *arr_oneline* is true (default: ``False``), then lists/tuples will be
+    encoded as arrays on a single line.
 
     To use a custom ``JSONEncoder`` subclass (e.g. one that overrides the
     ``.default()`` method to serialize additional types), specify it with
@@ -235,7 +239,7 @@ def dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True,
         skipkeys=skipkeys, ensure_ascii=ensure_ascii,
         check_circular=check_circular, allow_nan=allow_nan, indent=indent,
         separators=separators, default=default, sort_keys=sort_keys,
-        **kw).encode(obj)
+        arr_oneline=arr_oneline, **kw).encode(obj)
 
 
 _default_decoder = JSONDecoder(object_hook=None, object_pairs_hook=None)

Lib/json/encoder.py

@@ -104,7 +104,7 @@ class JSONEncoder(object):
     key_separator = ': '
     def __init__(self, *, skipkeys=False, ensure_ascii=True,
             check_circular=True, allow_nan=True, sort_keys=False,
-            indent=None, separators=None, default=None):
+            indent=None, separators=None, default=None, arr_oneline=False):
         """Constructor for JSONEncoder, with sensible defaults.
 
         If skipkeys is false, then it is a TypeError to attempt
@@ -129,6 +129,10 @@ def __init__(self, *, skipkeys=False, ensure_ascii=True,
         sorted by key; this is useful for regression tests to ensure
         that JSON serializations can be compared on a day-to-day basis.
 
+        If arr_oneline is true, then lists/tuples will be output as arrays
+        on a single line. If false, a newline character will be placed after each
+        array element.
+
         If indent is a non-negative integer, then JSON array
         elements and object members will be pretty-printed with that
         indent level.  An indent level of 0 will only insert newlines.
@@ -151,6 +155,7 @@ def __init__(self, *, skipkeys=False, ensure_ascii=True,
         self.allow_nan = allow_nan
         self.sort_keys = sort_keys
         self.indent = indent
+        self.arr_oneline = arr_oneline
         if separators is not None:
             self.item_separator, self.key_separator = separators
         elif indent is not None:
@@ -257,11 +262,12 @@ def floatstr(o, allow_nan=self.allow_nan,
             _iterencode = _make_iterencode(
                 markers, self.default, _encoder, indent, floatstr,
                 self.key_separator, self.item_separator, self.sort_keys,
-                self.skipkeys, _one_shot)
+                self.skipkeys, _one_shot, self.arr_oneline)
         return _iterencode(o, 0)
 
 def _make_iterencode(markers, _default, _encoder, _indent, _floatstr,
         _key_separator, _item_separator, _sort_keys, _skipkeys, _one_shot,
+        arr_oneline,
         ## HACK: hand-optimized bytecode; turn globals into locals
         ValueError=ValueError,
         dict=dict,
@@ -287,7 +293,10 @@ def _iterencode_list(lst, _current_indent_level):
         buf = '['
         if _indent is not None:
             _current_indent_level += 1
-            newline_indent = '\n' + _indent * _current_indent_level
+            if not arr_oneline:
+                newline_indent = '\n' + _indent * _current_indent_level
+            else:
+                newline_indent = ''
             separator = _item_separator + newline_indent
             buf += newline_indent
         else:
@@ -329,7 +338,8 @@ def _iterencode_list(lst, _current_indent_level):
                 raise
         if newline_indent is not None:
             _current_indent_level -= 1
-            yield '\n' + _indent * _current_indent_level
+            if not arr_oneline:
+                yield '\n' + _indent * _current_indent_level
         yield ']'
         if markers is not None:
             del markers[markerid]

Misc/NEWS.d/next/Library/2022-03-08-11-13-25.bpo-46958.2CkwDp.rst

@@ -0,0 +1,3 @@
+Added optional argument *list_oneline* to :meth:`json.dump` and
+:meth:`json.dumps` for printing array output on a single
+line. Patch by Daniel Marshall.