Write compiled bytecode inline with standard Python syntax.
HAX lets you write compiled bytecode inline with standard Python syntax.
HAX supports CPython 3.6–3.9.
To install, just run:
$ pip install hax
Consider the following function; it accepts a sequence of items, and returns a list with each item repeated twice:
from typing import List, Sequence, TypeVar T = TypeVar("T") def double(items: Sequence[T]) -> List[T]: out =  for item in items: out += item, item return out
(0, 1, 2) becomes
[0, 0, 1, 1, 2, 2].
We can make this function faster by keeping
out on the stack (instead of in a
local variable) and using the
LIST_APPEND op to build it. HAX makes it
simple to inline these instructions:
from hax import * @hax def double(items: Sequence[T]) -> List[T]: BUILD_LIST(0) for item in items: LOAD_FAST("item") DUP_TOP() LIST_APPEND(3) LIST_APPEND(2) RETURN_VALUE()
If you're up to the challenge of computing jump targets, the function can be further sped up by rewriting the for-loop in bytecode, removing all temporary variables, and operating entirely on the stack:
@hax def double(items: Sequence[T]) -> List[T]: BUILD_LIST(0) LOAD_FAST("items") GET_ITER() FOR_ITER(34) # When done, jump forward to RETURN_VALUE(). DUP_TOP() LIST_APPEND(3) LIST_APPEND(2) JUMP_ABSOLUTE(28) # Jump back to FOR_ITER(34). RETURN_VALUE()
It's important to realize that the functions HAX provides (
LOAD_FAST, ...) aren't just "emulating" their respective bytecode
@hax decorator detects them, and completely recompiles
double's code to use the actual ops that we've specified here!
These performance improvements are impossible to get from CPython's compiler and optimizer alone.
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