json_utils.py

# Copyright 2017 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Utilities for dealing with writing json strings.

json_utils wraps json.dump and json.dumps so that they can be used to safely
control the precision of floats when writing to json strings or files.
"""
import json
import re


def FormatFloat(json_str, float_digits):
  pattern = re.compile(r'\d+\.\d+')
  float_repr = '{:.' + '{}'.format(float_digits) + 'f}'
  def MRound(match):
    return float_repr.format(float(match.group()))
  return re.sub(pattern, MRound, json_str)


def Dump(obj, fid, float_digits=-1, **params):
  """Wrapper of json.dump that allows specifying the float precision used.

  Args:
    obj: The object to dump.
    fid: The file id to write to.
    float_digits: The number of digits of precision when writing floats out.
    **params: Additional parameters to pass to json.dumps.
  """
  json_str = Dumps(obj, float_digits, **params)
  fid.write(json_str)


def Dumps(obj, float_digits=-1, **params):
  """Wrapper of json.dumps that allows specifying the float precision used.

  Args:
    obj: The object to dump.
    float_digits: The number of digits of precision when writing floats out.
    **params: Additional parameters to pass to json.dumps.

  Returns:
    output: JSON string representation of obj.
  """
  json_str = json.dumps(obj, **params)
  if float_digits > -1:
    json_str = FormatFloat(json_str, float_digits)
  return json_str


def PrettyParams(**params):
  """Returns parameters for use with Dump and Dumps to output pretty json.

  Example usage:
    ```json_str = json_utils.Dumps(obj, **json_utils.PrettyParams())```
    ```json_str = json_utils.Dumps(
                      obj, **json_utils.PrettyParams(allow_nans=False))```

  Args:
    **params: Additional params to pass to json.dump or json.dumps.

  Returns:
    params: Parameters that are compatible with json_utils.Dump and
      json_utils.Dumps.
  """
  params['float_digits'] = 4
  params['sort_keys'] = True
  params['indent'] = 2
  params['separators'] = (',', ': ')
  return params