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

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, list_oneline=False, **kw):
     """Serialize ``obj`` as a JSON formatted stream to ``fp`` (a
     ``.write()``-supporting file-like object).
 
@@ -155,6 +155,9 @@ 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 *list_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 +175,8 @@ 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,
+            list_oneline=list_oneline, **kw).iterencode(obj)
     # could accelerate with writelines in some versions of Python, at
     # a debuggability cost
     for chunk in iterable:
@@ -182,7 +185,7 @@ 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, list_oneline=False, **kw):
     """Serialize ``obj`` to a JSON formatted ``str``.
 
     If ``skipkeys`` is true then ``dict`` keys that are not basic types
@@ -217,6 +220,9 @@ 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 *list_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 +241,7 @@ 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)
+        list_oneline=list_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, list_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 list_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.list_oneline = list_oneline
         if separators is not None:
             self.item_separator, self.key_separator = separators
         elif indent is not None:
@@ -254,11 +259,12 @@ def floatstr(o, allow_nan=self.allow_nan,
             _iterencode = _make_iterencode(
                 markers, self.default, _encoder, self.indent, floatstr,
                 self.key_separator, self.item_separator, self.sort_keys,
-                self.skipkeys, _one_shot)
+                self.skipkeys, _one_shot, self.list_oneline)
         return _iterencode(o, 0)
 
 def _make_iterencode(markers, _default, _encoder, _indent, _floatstr,
         _key_separator, _item_separator, _sort_keys, _skipkeys, _one_shot,
+        list_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 list_oneline:
+                newline_indent = '\n' + _indent * _current_indent_level
+            else:
+                newline_indent = ''
             separator = _item_separator + newline_indent
             buf += newline_indent
         else:
@@ -326,7 +335,8 @@ def _iterencode_list(lst, _current_indent_level):
                 yield from chunks
         if newline_indent is not None:
             _current_indent_level -= 1
-            yield '\n' + _indent * _current_indent_level
+            if not list_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 new optional list_oneline argument to json.dump() and json.dumps()
+which causes array output to be printed on a single line. Defaults to False
+if not passed.