#!/usr/bin/env python3
"""From a gist by Jannis Mainczyk
https://gist.github.com/jannismain/e96666ca4f059c3e5bc28abb711b5c92
"""
from __future__ import annotations
import json
[docs]
class CompactJSONEncoder(json.JSONEncoder):
"""A JSON Encoder that puts small containers on single lines."""
CONTAINER_TYPES = (list, tuple, dict)
"""Container datatypes include primitives or other containers."""
MAX_WIDTH = 80
"""Maximum width of a container that might be put on a single line."""
MAX_ITEMS = 6
"""Maximum number of items in container that might be put on single line."""
def __init__(self, *args, **kwargs):
# using this class without indentation is pointless
if kwargs.get("indent") is None:
kwargs["indent"] = 4
super().__init__(*args, **kwargs)
self.indentation_level = 0
[docs]
def encode(self, o):
"""Encode JSON object *o* with respect to single line lists."""
if isinstance(o, (list, tuple)):
return self._encode_list(o)
if isinstance(o, dict):
return self._encode_object(o)
if isinstance(o, float): # Use scientific notation for floats
return format(o, ".12g")
return json.dumps(
o,
skipkeys=self.skipkeys,
ensure_ascii=self.ensure_ascii,
check_circular=self.check_circular,
allow_nan=self.allow_nan,
sort_keys=self.sort_keys,
indent=self.indent,
separators=(self.item_separator, self.key_separator),
default=self.default if hasattr(self, "default") else None,
)
def _encode_list(self, o):
if self._put_on_single_line(o):
return "[" + ", ".join(self.encode(el) for el in o) + "]"
self.indentation_level += 1
output = [self.indent_str + self.encode(el) for el in o]
self.indentation_level -= 1
return "[\n" + ",\n".join(output) + "\n" + self.indent_str + "]"
def _encode_object(self, o):
if not o:
return "{}"
if self._put_on_single_line(o):
return (
"{ "
+ ", ".join(
f"{self.encode(k)}: {self.encode(el)}" for k, el in o.items()
)
+ " }"
)
self.indentation_level += 1
output = [
f"{self.indent_str}{json.dumps(k)}: {self.encode(v)}" for k, v in o.items()
]
self.indentation_level -= 1
return "{\n" + ",\n".join(output) + "\n" + self.indent_str + "}"
[docs]
def iterencode(self, o, **kwargs):
"""Required to also work with `json.dump`."""
return self.encode(o)
def _put_on_single_line(self, o):
return (
self._primitives_only(o)
and len(o) <= self.MAX_ITEMS
and len(str(o)) - 2 <= self.MAX_WIDTH
)
def _primitives_only(self, o: list | tuple | dict):
if isinstance(o, (list, tuple)):
return not any(isinstance(el, self.CONTAINER_TYPES) for el in o)
elif isinstance(o, dict):
return not any(isinstance(el, self.CONTAINER_TYPES) for el in o.values())
@property
def indent_str(self) -> str:
if isinstance(self.indent, int):
return " " * (self.indentation_level * self.indent)
elif isinstance(self.indent, str):
return self.indentation_level * self.indent
else:
raise ValueError(
f"indent must either be of type int or str (is: {type(self.indent)})"
)
if __name__ == "__main__":
import sys
if "--example" in sys.argv:
data = {
"compact_object": {"first": "element", "second": 2},
"compact_list": ["first", "second"],
"long_list": ["this", "is", "a", "rather", "long\nlist"],
"non_ascii": "汉语",
}
json.dump(data, sys.stdout, cls=CompactJSONEncoder, ensure_ascii=False)
exit()
json.dump(json.load(sys.stdin), sys.stdout)