Make generated patches deterministic (iterate dicts, not sets) #174
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This fixes the issue because it is specified for 3.6 and above. In python 3.6+, sets are not ordered, but dictionaries are. This means traversal will be stable across sessions, guaranteeing the same patches are generated. For python 3.5 and below, the stability of dictionary traversal is not a guarantee, unfortunately. But if you use CPython, the reference implementation of python, it does happen to be an implementation detail. See https://docs.python.org/2/library/stdtypes.html#dict.items for more details.
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Fixes #151
TL;DR
DiffBuildercurrently iterates sets of dict keys, and set iteration order is inherently unordered (and can vary across runs due to hash randomization). This yields non-deterministic patch order even for identical inputs.What Changes
Iterate the dicts directly, which preserves insertion order (language guarantee in Py≥3.6; implementation detail in CPython 2.7+).
Note
PYTHONHASHSEED. I can follow up with such a test, but I'd rather keep this PR minimal. Also it's kind of a mess to write this kind of test in a backwards-compatible way, down to Python 2.7.