Previously, hologram called str on all exceptions it gets while trying to decode union members, by using getattr(exc, 'message', str(exc)). Python's eager evaluation of expressions means that str(exc) is always called.
This is nice for error messaging about decode failures, but ends up potentially calling pprint.pformat via jsonschema.ValidationError.__str__, which is extremely slow.
This PR avoids that by deferring all calls to str until the exception's __str__ is called.
This improves performance by about an order of magnitude on union-heavy workloads from v0.0.8 (runtime from 660s -> 45s to parse a 6.3M manifest.json). That's still painfully slow, of course.
Previously, hologram called
stron all exceptions it gets while trying to decode union members, by usinggetattr(exc, 'message', str(exc)). Python's eager evaluation of expressions means thatstr(exc)is always called.This is nice for error messaging about decode failures, but ends up potentially calling
pprint.pformatviajsonschema.ValidationError.__str__, which is extremely slow.This PR avoids that by deferring all calls to
struntil the exception's__str__is called. This improves performance by about an order of magnitude on union-heavy workloads from v0.0.8 (runtime from 660s -> 45s to parse a 6.3M manifest.json). That's still painfully slow, of course.