Iterators without aclose() (rare) are notoriously problematic...

- So now aclose() is explicitly required.
- Since we effectively had an in-project `aclosing()` implementation, also
  removed async_generator dep.
- The new, better-annotated `aclosing()` triggered Pyright to alert on a few
  places where it was being applied to an iterable instead of an iterator.
  Fixed those, too.

docs/user.rst

@@ -38,9 +38,9 @@ pipeline out of individual sections. A ``PipelineSection`` is any object that is
 function. This currently includes the following types:
 
 AsyncIterables
-  Async iterables are valid only as the very first ``PipelineSection``. Subsequent
-  sections will use this async iterable as input source. Placing an ``AsyncIterable`` into the middle of
-  a sequence of pipeline sections, will cause a ``ValueError``.
+  Async iterables are valid only as the very first ``PipelineSection``, and must support the ``aclose()``
+  method (nearly all do). Subsequent sections will use this async iterable as input source. Placing an
+  ``AsyncIterable`` into the middle of a sequence of pipeline sections, will cause a ``ValueError``.
 Sections
   Any :class:`Section <slurry.sections.abc.Section>` abc subclass is a valid ``PipelineSection``, at any
   position in the pipeline.

pyproject.toml

@@ -23,7 +23,6 @@ classifiers = [
 
 
 [tool.poetry.dependencies]
-async-generator = "^1.10"
 python = "^3.8"
 trio = "^0.23.0"
 

slurry/_pipeline.py

@@ -5,11 +5,11 @@
 from contextlib import asynccontextmanager
 
 import trio
-from async_generator import aclosing
 
 from .sections.weld import weld
 from ._tap import Tap
 from ._types import PipelineSection
+from ._utils import aclosing
 
 class Pipeline:
     """The main Slurry ``Pipeline`` class.
@@ -54,7 +54,7 @@ async def _pump(self):
             output = weld(nursery, *self.sections)
 
             # Output to taps
-            async with aclosing(output) as aiter:
+            async with aclosing(output.__aiter__()) as aiter:
                 async for item in aiter:
                     self._taps = set(filter(lambda tap: not tap.closed, self._taps))
                     if not self._taps:

slurry/_types.py

@@ -1,10 +1,18 @@
-from typing import Any, AsyncIterable, Awaitable, Protocol, Tuple, Union, runtime_checkable
+from typing import Any, AsyncIterable, Awaitable, Protocol, Tuple, TypeVar, Union, runtime_checkable
 
-from .sections.abc import Section
+from .sections import abc
 
-PipelineSection = Union[AsyncIterable[Any], Section, Tuple["PipelineSection", ...]]
+PipelineSection = Union["AsyncIterableWithAcloseableIterator[Any]", "abc.Section", Tuple["PipelineSection", ...]]
+
+_T_co = TypeVar("_T_co", covariant=True)
 
 @runtime_checkable
 class SupportsAclose(Protocol):
-    def aclose(self) -> Awaitable[object]:
-        ...
+    def aclose(self) -> Awaitable[object]: ...
+
+class AcloseableAsyncIterator(SupportsAclose, Protocol[_T_co]):
+    def __anext__(self) -> Awaitable[_T_co]: ...
+    def __aiter__(self) -> "AcloseableAsyncIterator[_T_co]": ...
+
+class AsyncIterableWithAcloseableIterator(Protocol[_T_co]):
+    def __aiter__(self) -> AcloseableAsyncIterator[_T_co]: ...

slurry/_utils.py

@@ -1,15 +1,14 @@
-from typing import AsyncGenerator, AsyncIterator, TypeVar
+from typing import AsyncGenerator, TypeVar
 
-from ._types import SupportsAclose
+from ._types import AcloseableAsyncIterator
 
 from contextlib import asynccontextmanager
 
 _T = TypeVar("_T")
 
 @asynccontextmanager
-async def safe_aclosing(obj: AsyncIterator[_T]) -> AsyncGenerator[AsyncIterator[_T], None]:
+async def aclosing(obj: AcloseableAsyncIterator[_T]) -> AsyncGenerator[AcloseableAsyncIterator[_T], None]:
     try:
         yield obj
     finally:
-        if isinstance(obj, SupportsAclose):
-            await obj.aclose()
+        await obj.aclose()

slurry/environments/_multiprocessing.py

@@ -1,11 +1,12 @@
 """Implements a section that runs in an independent python proces."""
 
 from multiprocessing import Process, SimpleQueue
-from typing import AsyncIterable, Any, Awaitable, Callable, Optional, cast
+from typing import Any, Awaitable, Callable, Optional, cast
 
 import trio
 
 from ..sections.abc import SyncSection
+from .._types import AsyncIterableWithAcloseableIterator
 
 class ProcessSection(SyncSection):
     """ProcessSection defines a section interface with a synchronous
@@ -19,7 +20,9 @@ class ProcessSection(SyncSection):
         <https://docs.python.org/3/library/pickle.html#what-can-be-pickled-and-unpickled>`_.
     """
 
-    async def pump(self, input: Optional[AsyncIterable[Any]], output: Callable[[Any], Awaitable[None]]):
+    async def pump(
+        self, input: Optional[AsyncIterableWithAcloseableIterator[Any]], output: Callable[[Any], Awaitable[None]]
+    ):
         """
         The ``ProcessSection`` pump method works similar to the threaded version, however
         since communication between processes is not as simple as it is between threads,

slurry/environments/_threading.py

@@ -1,9 +1,10 @@
 """The threading module implements a synchronous section that runs in a background thread."""
-from typing import Any, AsyncIterable, Awaitable, Callable, Optional
+from typing import Any, Awaitable, Callable, Optional
 
 import trio
 
 from ..sections.abc import SyncSection
+from .._types import AsyncIterableWithAcloseableIterator
 
 
 class ThreadSection(SyncSection):
@@ -12,7 +13,7 @@ class ThreadSection(SyncSection):
     """
 
     async def pump(self,
-                   input: Optional[AsyncIterable[Any]],
+                   input: Optional[AsyncIterableWithAcloseableIterator[Any]],
                    output: Callable[[Any], Awaitable[None]]):
         """Runs the refine method in a background thread with synchronous input and output
         wrappers, which transparently bridges the input and outputs between the parent

slurry/environments/_trio.py

@@ -1,13 +1,16 @@
 """The Trio environment implements ``TrioSection``, which is a Trio-native 
 :class:`AsyncSection <slurry.sections.abc.AsyncSection>`."""
-from typing import Any, AsyncIterable, Awaitable, Callable, Optional
+from typing import Any, Awaitable, Callable, Optional
 
 from ..sections.abc import AsyncSection
+from .._types import AsyncIterableWithAcloseableIterator
 
 class TrioSection(AsyncSection):
     """Since Trio is the native Slurry event loop, this environment is simple to implement.
     The pump method does not need to do anything special to bridge the input and output. It
     simply delegates directly to the refine method, as the api is identical."""
-    async def pump(self, input: Optional[AsyncIterable[Any]], output: Callable[[Any], Awaitable[None]]):
+    async def pump(
+        self, input: Optional[AsyncIterableWithAcloseableIterator[Any]], output: Callable[[Any], Awaitable[None]]
+    ):
         """Calls refine."""
         await self.refine(input, output)

slurry/sections/_buffers.py

@@ -1,12 +1,13 @@
 """Pipeline sections with age- and volume-based buffers."""
 from collections import deque
 import math
-from typing import Any, AsyncIterable, Callable, Optional, Sequence
+from typing import Any, Callable, Optional, Sequence
 
 import trio
-from async_generator import aclosing
 
 from ..environments import TrioSection
+from .._types import AsyncIterableWithAcloseableIterator
+from .._utils import aclosing
 
 class Window(TrioSection):
     """Window buffer with size and age limits.
@@ -26,13 +27,13 @@ class Window(TrioSection):
     :param max_size: The maximum buffer size.
     :type max_size: int
     :param source: Input when used as first section.
-    :type source: Optional[AsyncIterable[Any]]
+    :type source: Optional[AsyncIterableWithAcloseableIterator[Any]]
     :param max_age: Maximum item age in seconds. (default: unlimited)
     :type max_age: float
     :param min_size: Minimum amount of items in the buffer to trigger an output.
     :type min_size: int
     """
-    def __init__(self, max_size: int, source: Optional[AsyncIterable[Any]] = None, *,
+    def __init__(self, max_size: int, source: Optional[AsyncIterableWithAcloseableIterator[Any]] = None, *,
                  max_age: float = math.inf,
                  min_size: int = 1):
         super().__init__()
@@ -51,7 +52,7 @@ async def refine(self, input, output):
 
         buf = deque()
 
-        async with aclosing(source) as aiter:
+        async with aclosing(source.__aiter__()) as aiter:
             async for item in aiter:
                 now = trio.current_time()
                 buf.append((item, now))
@@ -80,7 +81,7 @@ class Group(TrioSection):
     :param interval: Time in seconds from when an item arrives until the buffer is sent.
     :type interval: float
     :param source: Input when used as first section.
-    :type source: Optional[AsyncIterable[Any]]
+    :type source: Optional[AsyncIterableWithAcloseableIterator[Any]]
     :param max_size: Maximum number of items in buffer, which when reached, will cause the buffer
         to be sent.
     :type max_size: int
@@ -89,7 +90,7 @@ class Group(TrioSection):
     :param reducer: Optional reducer function used to transform the buffer to a single value.
     :type reducer: Optional[Callable[[Sequence[Any]], Any]]
     """
-    def __init__(self, interval: float, source: Optional[AsyncIterable[Any]] = None, *,
+    def __init__(self, interval: float, source: Optional[AsyncIterableWithAcloseableIterator[Any]] = None, *,
                  max_size: Optional[int] = None,
                  mapper: Optional[Callable[[Any], Any]] = None,
                  reducer: Optional[Callable[[Sequence[Any]], Any]] = None):
@@ -111,7 +112,7 @@ async def refine(self, input, output):
 
             send_channel, receive_channel = trio.open_memory_channel(0)
             async def pull_task():
-                async with send_channel, aclosing(source) as aiter:
+                async with send_channel, aclosing(source.__aiter__()) as aiter:
                     async for item in aiter:
                         await send_channel.send(item)
             nursery.start_soon(pull_task)
@@ -152,9 +153,9 @@ class Delay(TrioSection):
     :param interval: Number of seconds that each item is delayed.
     :type interval: float
     :param source: Input when used as first section.
-    :type source: Optional[AsyncIterable[Any]]
+    :type source: Optional[AsyncIterableWithAcloseableIterator[Any]]
     """
-    def __init__(self, interval: float, source: Optional[AsyncIterable[Any]] = None):
+    def __init__(self, interval: float, source: Optional[AsyncIterableWithAcloseableIterator[Any]] = None):
         super().__init__()
         self.source = source
         self.interval = interval
@@ -169,7 +170,7 @@ async def refine(self, input, output):
         buffer_input_channel, buffer_output_channel = trio.open_memory_channel(math.inf)
 
         async def pull_task():
-            async with buffer_input_channel, aclosing(source) as aiter:
+            async with buffer_input_channel, aclosing(source.__aiter__()) as aiter:
                 async for item in aiter:
                     await buffer_input_channel.send((item, trio.current_time() + self.interval))
 

slurry/sections/_combiners.py

@@ -3,11 +3,11 @@
 import itertools
 
 import trio
-from async_generator import aclosing
 
 from ..environments import TrioSection
 from .weld import weld
 from .._types import PipelineSection
+from .._utils import aclosing
 
 class Chain(TrioSection):
     """Chains input from one or more sources. Any valid ``PipelineSection`` is an allowed source.
@@ -40,7 +40,7 @@ async def refine(self, input, output):
             sources = self.sources
         async with trio.open_nursery() as nursery:
             for source in sources:
-                async with aclosing(weld(nursery, source)) as agen:
+                async with aclosing(weld(nursery, source).__aiter__()) as agen:
                     async for item in agen:
                         await output(item)
 
@@ -66,7 +66,7 @@ async def refine(self, input, output):
         async with trio.open_nursery() as nursery:
 
             async def pull_task(source):
-                async with aclosing(weld(nursery, source)) as aiter:
+                async with aclosing(weld(nursery, source).__aiter__()) as aiter:
                     async for item in aiter:
                         await output(item)
 
@@ -155,7 +155,8 @@ class ZipLatest(TrioSection):
         default value to output, until an input has arrived on a source. Defaults to ``None``.
     :type default: Any
     :param monitor: Additional asynchronous sequences to monitor.
-    :type monitor: Optional[Union[AsyncIterable[Any], Sequence[AsyncIterable[Any]]]]
+    :type monitor: Optional[Union[AsyncIterableWithAcloseableIterator[Any],
+        Sequence[AsyncIterableWithAcloseableIterator[Any]]]]
     :param place_input: Position of the pipeline input source in the output tuple. Options:
         ``'first'`` (default)|``'last'``
     :type place_input: string
@@ -203,7 +204,7 @@ async def refine(self, input, output):
         async with trio.open_nursery() as nursery:
 
             async def pull_task(index, source, monitor=False):
-                async with aclosing(weld(nursery, source)) as aiter:
+                async with aclosing(weld(nursery, source).__aiter__()) as aiter:
                     async for item in aiter:
                         results[index] = item
                         ready[index] = True