a patchy interface to allow use in contexts

[graingert]

import contextlib
from concurrent import futures

import patchy

def sample():
    return 1

patchy.prepare(
    sample,
    """\
    @@ -1,2 +1,2 @@
    def sample():
    -    return 1
    +    return 9001
    """,
)

def run(patch):
    with prepared_patch() if patch else contextlib.nullcontext():
        return target()

with futures.ThreadPoolExecutor(max_workers=999) as executor:
    assert list(executor.map(run, [i % 2 for i in range(100)))) == [1, 9001, 1, 9001 ...]

[graingert]

eg it would have to replace .__code__ with something that delegated to a ContextVar that either ran the old code or the patch, then the ContextVar could switch between them

[graingert]

Hmm maybe it would be better to just document how people could do it themselves with existing patchy:

import contextlib
from concurrent import futures

import patchy

def sample():
    return 1

sample_ctx = ContextVar('sample', default=1)

patchy.patch(
    sample,
    f"""\
    @@ -1,2 +1,2 @@
    def sample():
    -    return 1
    +    return importlib.import_module({__name__!r}).sample_ctx.get()
    """,
)


def contextvar_context_manager(ctx):
    @contextlib.contextmanager
    def cm(update):
        token = ctx.set(update)
        try:
            yield
        finally:
            ctx.reset(token)

sample_ctx_context_manager = contextvar_context_manager(sample_ctx)

def run(patch):
    with sample_ctx_context_manager(9001) if patch else contextlib.nullcontext():
        return target()

with futures.ThreadPoolExecutor(max_workers=999) as executor:
    assert list(executor.map(run, [i % 2 for i in range(100)))) == [1, 9001, 1, 9001 ...]

[adamchainz]

Yeah I don't think replacing __code__ with something that does dispatch is possible.

Anyway... why do you want this?

[adamchainz]

Gonna close for now, if someone has this problem again they can find this.