Use json instead of simplejson

[ijl]

itsdangerous and by extension flask, starlette, and others use simplejson if it's installed due to:

try:
    import simplejson as json
except ImportError:
    import json

Is there still a reason to use simplejson? I don't know of a feature or compatibility reason.

The reason I have seen mentioned is better performance. That is not the case with at least python3.6+ and a modern distribution (that probably compiled python with PGO and LTO) with simplejson compiled. See these benchmarks.

If simplejson is installed in a container without a compiler, it falls back to running in pure Python. This is a footgun:

In [1]: import json, simplejson

In [2]: data = list(range(0, 100000))

In [3]: %timeit json.dumps(data)
17.4 ms ± 1.14 ms per loop (mean ± std. dev. of 7 runs, 100 loops each)

In [4]: %timeit simplejson.dumps(data)
89.4 ms ± 7.21 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

It seems preferable to just use json.

[CoburnJoe]

json was added to Python 2.6, so the main reason to use simplejson is backwards compatibility with Python 2.4+ (although, as someone who occasionally has to maintain Python 2.4 code, the sooner it dies the better).

Considering the oldest test suite on this project runs on Python 2.7, it seems a good candidate to refactor this.

[davidism]

Yeah, I'm fairly ok with this once we drop Python 2.

[dkarp0]

When using the 2.0.0a1 build my tests failed and I've narrowed it down to this change.

One big difference between json and simplejson is that the latter supports serializing Decimal types. Flask-sqlalchemy uses Decimal, so this change might affect quite a few people when they upgrade.