Comment by swordfeng | Hacker News Reader

Comment by swordfeng | Hacker News Reader

I was once trying to do something even crazier: exposing full python accessibility to node.js, using proxies. So that you can use python objects and functions as native javascript objects and functions. It is feasible because the languages and runtimes share a number of common designs.

There were several tough things however. The first was error handling. Yes you can catch exceptions in native code and convert it to exceptions in the other language, but it's not straightforward to keep stacktraces. The second was circular references between runtimes. Since references across boundaries are global, garbage collector on either side could not reclaim circularly referenced objects. Although this could be resolved by manually breaking up the circle, it could be better to have weak references. (Or maybe other utilities, idk what would be more elegant.) The third was that js has no operator overloading, so I had to use .__add__() for example to call the python add operator.

One line example: https://github.com/swordfeng/pyjs/blob/master/test/jsobject.... It's a toy project I did years ago and not even compiling now. Also I was wondering if anyone really need to do things in this way, given there are bunch of popular and stable RPC libraries. But I was happy to learn something about underlying cpython and v8 from it.

> The third was that js has no operator overloading, so I had to use .__add__() for example to call the python add operator.

I expect this wouldn't have worked in the long run as these methods are often just part of the protocol e.g. even `a == b` will try `type(a).__eq__(a, b)` then fall back to `type(b).__eq__(a)` (~~and then it'll do some weird stuff with type names IIRC~~[0]).

And most operators are not considered symmetric so the fallback is not the same as the initial (even `+` has `__add__` and `__radd__`, also `__radd__` might be called first depending on the relationship between type(a) and type(b)).

And then there's the "operations" which fallback to entirely different protocols e.g. `in` will first try to use `__contains__`, if that doesn't exist it uses `iter()` which tries to use `__iter__` but if that doesn't exist it falls back to calling `__getitem__` with non-negative sequential integer.

Which is why sometimes you define `__getitem__` for a pseudo-mapping convenience and then you get weird blowups that it's been called with `0` (you only ever expected string-keys). Because someone somewhere used `in` on your object and you hadn't defined `__iter__` let alone `__contains__`.

Good times.

[0] I misremembered: it's for ordering (not equality) in Python 2[1] `a < b` will first invoke `type(a).__lt__(a, b)`, then if that's not implemented fall back to `type(b).__ge__(a)`, and if that's not implemented either it'll fall back to a few hard-coded cases (e.g. None is smaller than everything) and finally to `(type(a).__name__, id(a)) < (type(b).__name__, id(b))`. That is the order of independent types with no ordering defined is the lexicographic order of their type names, and if they're of the same type it's their position in memory

[1] where there's always an ordering relationship between two objects, one of the things I'm most graceful Python 3 removed even if it's sometimes inconvenient

This is great. I wanted to do something similar so that I could render Django templates in native JSX.

Any idea which of those RPC libraries could help achieve this? I'd love a Django model instance that could be used seamlessly in a JSX template.

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