[chc]

The place where I work uses it for back-end report generation. In my experience, PyPy's claimed speed benefits are very realistic. For most of our code, we get about a 3x speedup. For some areas of code, we get up to a 7x speedup. The only compatibility issues we've run into stemmed from mistakes on our part (e.g. all dicts are effectively OrderedDicts in PyPy, but your code will break in CPython if you rely on that implementation detail).

As a side note, for some reason, it's terrible for pytest — your tests will take literally 100x as long. If you trust PyPy's compatibility, I'd recommend running your tests with CPython even if you run PyPy in production.

[ris]

> all dicts are effectively OrderedDicts in PyPy, but your code will break in CPython if you rely on that implementation detail

Actually since CPython 3.6 (or maybe it's 3.5?) the same is true in CPython too, though I'd personally still advocate specifying OrderedDict if you particularly require that property anyway.