Preserve float formatting when pretty formatting

pre_commit_hooks/pretty_format_json.py

@@ -4,10 +4,74 @@
 import json
 import sys
 from difflib import unified_diff
+from typing import Any
+from typing import Iterator
 from typing import Mapping
 from typing import Sequence
 
 
+class FloatString(float):
+    def __init__(self, str_value: str):
+        self.str_value = str_value
+
+    def __repr__(self):
+        return self.str_value
+
+
+def float_parser(value: str) -> FloatString:
+    return FloatString(value)
+
+
+class FloatPreservingEncoder(json.JSONEncoder):
+    def iterencode(self, o: Any, _one_shot: bool = ...) -> Iterator[str] | str:
+        if self.check_circular:
+            markers = {}
+        else:
+            markers = None
+        if self.ensure_ascii:
+            _encoder = json.encoder.encode_basestring_ascii
+        else:
+            _encoder = json.encoder.encode_basestring
+
+        def floatstr(
+            o,
+            allow_nan=self.allow_nan,
+            _repr=FloatString.__repr__,
+            _inf=json.encoder.INFINITY,
+            _neginf=-json.encoder.INFINITY,
+        ):
+
+            if o != o:
+                text = 'NaN'
+            elif o == _inf:
+                text = 'Infinity'
+            elif o == _neginf:
+                text = '-Infinity'
+            else:
+                return _repr(o)
+
+            if not allow_nan:
+                raise ValueError(
+                    'Out of range float values are not JSON compliant: ' + repr(o),
+                )
+
+            return text
+
+        _iterencode = json.encoder._make_iterencode(
+            markers,
+            self.default,
+            _encoder,
+            self.indent,
+            floatstr,
+            self.key_separator,
+            self.item_separator,
+            self.sort_keys,
+            self.skipkeys,
+            _one_shot,
+        )
+        return _iterencode(o, 0)
+
+
 def _get_pretty_format(
         contents: str,
         indent: str,
@@ -23,9 +87,10 @@ def pairs_first(pairs: Sequence[tuple[str, str]]) -> Mapping[str, str]:
             after.sort()
         return dict(before + after)
     json_pretty = json.dumps(
-        json.loads(contents, object_pairs_hook=pairs_first),
+        json.loads(contents, object_pairs_hook=pairs_first, parse_float=float_parser),
         indent=indent,
         ensure_ascii=ensure_ascii,
+        cls=FloatPreservingEncoder,
     )
     return f'{json_pretty}\n'
 

testing/resources/float_formatting.json

@@ -0,0 +1,12 @@
+{
+  "exponential": 1e9,
+  "high_precision": 4.4257052820783003,
+  "list": [
+    1e9,
+    4.4257052820783003
+  ],
+  "mapping": {
+    "exponential": 1e9,
+    "high_precision": 4.4257052820783003
+  }
+}

tests/pretty_format_json_test.py

@@ -23,6 +23,7 @@ def test_parse_num_to_int():
         ('unsorted_pretty_formatted_json.json', 1),
         ('non_ascii_pretty_formatted_json.json', 1),
         ('pretty_formatted_json.json', 0),
+        ('float_formatting.json', 0),
     ),
 )
 def test_main(filename, expected_retval):