feat(Python): Support caching const variables #6134
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fabiomadge
reviewed
Mar 4, 2025
| if (!createBody) { return null; } | ||
| methodWriter.WriteLine(isStatic ? $"@{DafnyRuntimeModule}.classproperty" : "@property"); | ||
| // if (isConst and cacheConstVariablesCliFlag) |
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I think always caching is ok, so let's remove the remains of the flag everywhere.
| // Setting this to 1 means that only 1 input/output pair is cached. | ||
| // Since const methods only take `self` or `instance` and no other parameters, there is only 1 input/output pair. | ||
| // maxsize can be fixed to 1. | ||
| methodWriter.WriteLine("@lru_cache(maxsize=1)"); |
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Did you test this with inheritance?
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A child class accessing an inherited cached property results in a cache miss. It overwrites the cached value from the parent class.
Do you mean something like creating a global/class-level variable, then storing the cached value there? |
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What was changed?
This is a proposal / proof of concept, not a ready-to-merge PR.
If the Dafny team likes this approach, I'll add a CLI argument to enable writing cache decorators on const variables.
Problem:
I'm seeing slow performance in Python when accessing complex const variables: example.
Some code that takes ~5-10 minutes in other languages takes ~40 minutes in Python.
I suspect other languages have some cache-like optimization for frequently-called methods, while Python is recomputing the value each time.
Since these variables are const, their values don't need to be recomputed every time they're accessed.
How has this been tested?
I tested code compiled with this change and its performance was now on-par with other languages.
By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.