JSON encoding of non-finite floats

[LukasBoersma]

As described in #983, the JSON output is currently generating invalid JSON when non-finite floats (like NaN or Infinity) are included.

As @sbrugman suggested, I added a config option to switch between three behaviours:

• PYTHON_NATIVE: Use Python's default behaviour and generate the invalid JSON (as before)
• NULL: Encode non-finite numbers as null values.
• STRING: Stringify non-finite numbers (for example, NaN becomes the string "nan")

I made the null output the new default because it seems less surprising to encounter a null value when parsing numbers in the JSON compared to a "nan" string. I see that there is also an argument to make the old behaviour the default, to ensure 100% compatibility with existing code. Please let me know what you think should be the default.

Summary of the changes

• I added an enum JsonNonFiniteEncoding with the three options listed above
• I added an json_non_finite_encoding field in the Settings class
• In the encode_it method that already manages the JSON-encoding of all values, I added special handling for non-finite floats, which encodes the values according to the configuration.

The changes should not break anything except that the JSON output will now contain null values instead of the raw "NaN" entries that violate the standard.

Example usage

import pandas as pd
from pandas_profiling import ProfileReport
from pandas_profiling.config import Settings, JsonNonFiniteEncoding

df = pd.DataFrame([1, 1, 1], columns=["a"])

profile = ProfileReport(df, title="Pandas Profiling Report", minimal=True)

profile.config.json_non_finite_encoding = JsonNonFiniteEncoding.STRING

print(profile.to_json())

Gives the following output:

[...]
"kurtosis": "nan",
[...]

When choosing the NULL config option, it would be:

"kurtosis": null,

And with the PYTHON_NATIVE option it would be:

"kurtosis": NaN,

[alexbarros]

the same comment, can you update the string one?

[alexbarros]

Other than the commitlint issues looks good to me, can you fix it so we can merge this?
Also, can you add some tests?

[chanedwin]

@LukasBoersma could you change this PR to merge into develop instead of spark-branch? it isn't a spark specific issue