I need to write a test in Python to validate that the payload I am returning is a valid JSON.
import json
s = '{"position": NaN, "score": 0.3}'
json.loads(s)
the code above doesn't throw an exception, while the string is obviously not a valid JSON according to my backend friend and jsonlint.com/.
What should I do?
By default json.loads accepts '-Infinity', 'Infinity', 'NaN' as values. But you can control this by using parse_constant parameter.
Quoting from the documentation,
if it specified, will be called with one of the following strings: '
-Infinity', 'Infinity', 'NaN'. This can be used to raise an exception if invalid JSON numbers are encountered
You can use parse_constant, documentation says:
if specified, will be called with one of the following strings: -Infinity, Infinity, NaN. This can be used to raise an exception if invalid JSON numbers are encountered.
For example:
import json
s = '{"position": NaN, "score": 0.3}'
def validate(val):
if val == 'NaN':
raise ValueError('Nan is not allowed')
return val
print(json.loads(s, parse_constant=validate))
According to json.JSONDecoder documentation - "It also understands NaN, Infinity, and -Infinity as their corresponding float values, which is outside the JSON spec. [...] parse_constant, if specified, will be called with one of the following strings: '-Infinity', 'Infinity', 'NaN'. This can be used to raise an exception if invalid JSON numbers are encountered."
import json
def exc(x):
raise ValueError(f"{x} is not a valid JSON object")
s = '{"position": Infinity, "score": 0.3}'
d = json.loads(s, parse_constant=exc)
print(d)
