Load an empty string as a JSON in Python3

Question

I can not use an empty string in json.loads().

Python 3.6.4 (default, Jan  5 2018, 02:13:53) 
[GCC 7.2.0] on linux
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>>> import json
>>> json.loads('')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Is there a way to prevent the JSDONDecodeError and just return a default value (e.g. empty dict, list or None)? if json.loads() handle an empty string?

The background of my question is I read file contents and parse them with json.loads. But sometimes the files are empty (size=0). This is ok and not an error. But I don't want to check the file size or content size before using json.loads().

Ignacio Vazquez-Abrams · Accepted Answer · 2018-02-09 16:44:55Z

13

Use coalescing to pass it something valid.

json.loads('' or 'null')

answered Feb 9, 2018 at 16:44

Ignacio Vazquez-Abrams

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5 Comments

buhtz Over a year ago

I tried to find an official python document explaining that concept. But couldn't find one. Can you give a hint?

Ignacio Vazquez-Abrams Over a year ago

docs.python.org/3/reference/expressions.html#boolean-operations

buhtz Over a year ago

This is a technical reference and not an explanation of the "coalescing" concept.

Ignacio Vazquez-Abrams Over a year ago

"The expression x or y first evaluates x; if x is true, its value is returned; otherwise, y is evaluated and the resulting value is returned."

Ctrl-C Over a year ago

What you may want is: json.loads('' or '{}') - returns an empty dict instead of None. But this depends on your case of course.

LiLika · Accepted Answer · 2022-12-22 06:16:57Z

0

To give another way that worked for me, I used the inline if which returns an empty string if there is no data to load: As seen below I wanted to load the request form data which is the session id

session_id = json.loads(request.form['session_id']) if request.form['session_id'] else ''

answered Dec 22, 2022 at 6:16

LiLika

497 bronze badges

1 Comment

Sanket Over a year ago

This will still fail if request.form['session_id'] is empty or None. As in else part you are again passing '' which leads to exception @LiLika

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