Add as_async_generator.

scrapy/utils/asyncgen.py

@@ -1,5 +1,17 @@
+import collections
+
+
 async def collect_asyncgen(result):
     results = []
     async for x in result:
         results.append(x)
     return results
+
+
+async def as_async_generator(it):
+    if isinstance(it, collections.abc.AsyncIterator):
+        async for r in it:
+            yield r
+    else:
+        for r in it:
+            yield r

tests/test_utils_asyncgen.py

@@ -0,0 +1,20 @@
+from twisted.trial import unittest
+
+from scrapy.utils.asyncgen import as_async_generator, collect_asyncgen
+from scrapy.utils.defer import deferred_f_from_coro_f
+
+
+class AsyncgenUtilsTest(unittest.TestCase):
+    @deferred_f_from_coro_f
+    async def test_as_async_generator(self):
+        ag = as_async_generator(range(42))
+        results = []
+        async for i in ag:
+            results.append(i)
+        self.assertEqual(results, list(range(42)))
+
+    @deferred_f_from_coro_f
+    async def test_collect_asyncgen(self):
+        ag = as_async_generator(range(42))
+        results = await collect_asyncgen(ag)
+        self.assertEqual(results, list(range(42)))