python JSON array newlines

Question

I have a large dictionary that has some large array data in it:

d = {\'something\': {\'else\': \'x\'}, \'longnumbers\': [1,2,3,4,54,6,67,7,7,8,8,8,6,4,3,3,5,6,7,         


        

Answer 1

Ugh, should really be an option for specifying different indents for the two different JSON container types by now. An alternative approach if you want to stay compatible with the core Python JSON lib is to override the function (_make_iterencode() currently) in that lib that is responsible for handling indent.

Had a crack at reimplementation of _make_iterencode(). Only had to change a few lines to make the indent option, optionally take a tuple (hash-indent, array-indent). But unfortunately have to replace an entire _make_iterencode() which turns out to be pretty big and poorly decomposed. Anyway, following works for 3.4-3.6:

import sys
import json

dat = {"b": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], "a": 1, "c": "x"}
indent = 2
print(json.dumps(dat, indent=indent))

if sys.version_info.major == 3 and 4 <= sys.version_info.minor <= 6:
  import _make_iterencode
  json.encoder._make_iterencode = _make_iterencode._make_iterencode
  indent = (2, None)

print(json.dumps(dat, indent=indent))

Gives:

{
  "c": "x",
  "a": 1,
  "b": [
    1,
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    9,
    10
  ]
}
{
  "c": "x",
  "a": 1,
  "b": [1,2,3,4,5,6,7,8,9,10]
}

Answer 2

@jterrace's answer was written for Python 2, which has since deprecated for Python 3 with changes to types. So, with all due credit to his answer, I tweaked it a tad bit for my personal use & compatibility with Python 3, including support for tuples as lists:

import numpy

INDENT = 3
SPACE = " "
NEWLINE = "\n"

# Changed basestring to str, and dict uses items() instead of iteritems().
def to_json(o, level=0):
  ret = ""
  if isinstance(o, dict):
    ret += "{" + NEWLINE
    comma = ""
    for k, v in o.items():
      ret += comma
      comma = ",\n"
      ret += SPACE * INDENT * (level + 1)
      ret += '"' + str(k) + '":' + SPACE
      ret += to_json(v, level + 1)

    ret += NEWLINE + SPACE * INDENT * level + "}"
  elif isinstance(o, str):
    ret += '"' + o + '"'
  elif isinstance(o, list):
    ret += "[" + ",".join([to_json(e, level + 1) for e in o]) + "]"
  # Tuples are interpreted as lists
  elif isinstance(o, tuple):
    ret += "[" + ",".join(to_json(e, level + 1) for e in o) + "]"
  elif isinstance(o, bool):
    ret += "true" if o else "false"
  elif isinstance(o, int):
    ret += str(o)
  elif isinstance(o, float):
    ret += '%.7g' % o
  elif isinstance(o, numpy.ndarray) and numpy.issubdtype(o.dtype, numpy.integer):
    ret += "[" + ','.join(map(str, o.flatten().tolist())) + "]"
  elif isinstance(o, numpy.ndarray) and numpy.issubdtype(o.dtype, numpy.inexact):
    ret += "[" + ','.join(map(lambda x: '%.7g' % x, o.flatten().tolist())) + "]"
  elif o is None:
    ret += 'null'
  else:
    raise TypeError("Unknown type '%s' for json serialization" % str(type(o)))
  return ret

Answer 3

I ended up just writing my own JSON serializer:

import numpy

INDENT = 3
SPACE = " "
NEWLINE = "\n"

def to_json(o, level=0):
    ret = ""
    if isinstance(o, dict):
        ret += "{" + NEWLINE
        comma = ""
        for k,v in o.iteritems():
            ret += comma
            comma = ",\n"
            ret += SPACE * INDENT * (level+1)
            ret += '"' + str(k) + '":' + SPACE
            ret += to_json(v, level + 1)

        ret += NEWLINE + SPACE * INDENT * level + "}"
    elif isinstance(o, basestring):
        ret += '"' + o + '"'
    elif isinstance(o, list):
        ret += "[" + ",".join([to_json(e, level+1) for e in o]) + "]"
    elif isinstance(o, bool):
        ret += "true" if o else "false"
    elif isinstance(o, int):
        ret += str(o)
    elif isinstance(o, float):
        ret += '%.7g' % o
    elif isinstance(o, numpy.ndarray) and numpy.issubdtype(o.dtype, numpy.integer):
        ret += "[" + ','.join(map(str, o.flatten().tolist())) + "]"
    elif isinstance(o, numpy.ndarray) and numpy.issubdtype(o.dtype, numpy.inexact):
        ret += "[" + ','.join(map(lambda x: '%.7g' % x, o.flatten().tolist())) + "]"
    elif o is None:
        ret += 'null'
    else:
        raise TypeError("Unknown type '%s' for json serialization" % str(type(o)))
    return ret