Unescaped quote marks in to_json output when run on multi indexed object

[beegibson]

Code Sample

import pandas as pd
import numpy as np

arrays = [['bar', 'bar', 'baz', 'baz', 'foo', 'foo', 'qux', 'qux'], ['one',
    'two', 'one', 'two', 'one', 'two', 'one', 'two']]

tuples = list(zip(*arrays))
index = pd.MultiIndex.from_tuples(tuples, names=['first', 'second'])
series = pd.Series(np.random.randn(8), index=index)

print(series.to_json())

Output:

{"["bar","one"]":-0.0591166327,"["bar","two"]":0.871145093,"["baz","one"]":0.61280938,"["baz","two"]":0.3848564991,"["foo","one"]":-0.8986592304,"["foo","two"]":-0.4631529084,"["qux","one"]":-1.3482521044,"["qux","two"]":0.5209236198}

Problem description

The output contains unescaped quotation marks, which makes the output invalid json.

Expected Output

Quote marks should be escaped, for example:

{"[\"bar\",\"one\"]":-0.0591166327,"[\"bar\",\"two\"]":0.871145093,"[\"baz\",\"one\"]":0.61280938,"[\"baz\",\"two\"]":0.3848564991,"[\"foo\",\"one\"]":-0.8986592304,"[\"foo\",\"two\"]":-0.4631529084,"[\"qux\",\"one\"]":-1.3482521044,"[\"qux\",\"two\"]":0.5209236198}

Output of pd.show_versions()

I reproduced it in pandas install from master:

INSTALLED VERSIONS ------------------ commit: None python: 3.6.0.final.0 python-bits: 64 OS: Linux OS-release: 4.8.8-200.fc24.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_AU.UTF-8 LOCALE: en_AU.UTF-8

pandas: 0.19.0+401.g8452080
nose: None
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.2
numpy: 1.12.0
scipy: None
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2016.10
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
pandas_datareader: None

[jreback]

thanks this was just reported and is a duplicate of #15273

welcome to do a pull request to fix!