From d66d52d3ed8aab0b4f126169c2855d00f4053907 Mon Sep 17 00:00:00 2001
From: Andrey Rakhmatullin <wrar@wrar.name>
Date: Tue, 2 Feb 2021 15:21:12 +0500
Subject: [PATCH] Add process_iterable_helper.

---
 scrapy/utils/middlewares.py     | 35 +++++++++++++
 tests/test_utils_middlewares.py | 87 +++++++++++++++++++++++++++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 scrapy/utils/middlewares.py
 create mode 100644 tests/test_utils_middlewares.py

diff --git a/scrapy/utils/middlewares.py b/scrapy/utils/middlewares.py
new file mode 100644
index 000000000..da28e0ddf
--- /dev/null
+++ b/scrapy/utils/middlewares.py
@@ -0,0 +1,35 @@
+# coding: utf-8
+import inspect
+
+
+def process_normal_iterable_helper(it, in_predicate=None, out_predicate=None, processor=None):
+    for o in it:
+        if in_predicate and not in_predicate(o):
+            continue
+        if processor is not None:
+            o = processor(o)
+        if out_predicate and not out_predicate(o):
+            continue
+        yield o
+
+
+async def process_async_iterable_helper(it, in_predicate=None, out_predicate=None, processor=None):
+    async for o in it:
+        if in_predicate and not in_predicate(o):
+            continue
+        if processor is not None:
+            o = processor(o)
+        if out_predicate and not out_predicate(o):
+            continue
+        yield o
+
+
+def process_iterable_helper(it, in_predicate=None, out_predicate=None, processor=None):
+    """
+    For each item in the iterable: skips it if in_predicate is False, applies processor,
+    skips the result if out_predicate is False, else yields it.
+    """
+    if inspect.isasyncgen(it):
+        return process_async_iterable_helper(it, in_predicate, out_predicate, processor)
+    else:
+        return process_normal_iterable_helper(it, in_predicate, out_predicate, processor)
diff --git a/tests/test_utils_middlewares.py b/tests/test_utils_middlewares.py
new file mode 100644
index 000000000..d395ba1a9
--- /dev/null
+++ b/tests/test_utils_middlewares.py
@@ -0,0 +1,87 @@
+import collections
+
+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
+from scrapy.utils.middlewares import process_iterable_helper
+
+
+def predicate1(o):
+    return bool(o % 2)
+
+
+def predicate2(o):
+    return o < 10
+
+
+def processor(o):
+    return o * 2
+
+
+class ProcessIterableHelperNormalTest(unittest.TestCase):
+
+    def test_normal_in_predicate(self):
+        iterable1 = iter([1, 2, 3])
+        iterable2 = process_iterable_helper(iterable1, in_predicate=predicate1)
+        self.assertIsInstance(iterable2, collections.abc.Iterable)
+        list2 = list(iterable2)
+        self.assertEqual(list2, [1, 3])
+
+    def test_normal_out_predicate(self):
+        iterable1 = iter([1, 2, 10, 3, 15])
+        iterable2 = process_iterable_helper(iterable1, out_predicate=predicate2)
+        self.assertIsInstance(iterable2, collections.abc.Iterable)
+        list2 = list(iterable2)
+        self.assertEqual(list2, [1, 2, 3])
+
+    def test_normal_processor(self):
+        iterable1 = iter([1, 2, 3])
+        iterable2 = process_iterable_helper(iterable1, processor=processor)
+        self.assertIsInstance(iterable2, collections.abc.Iterable)
+        list2 = list(iterable2)
+        self.assertEqual(list2, [2, 4, 6])
+
+    def test_normal_combined(self):
+        iterable1 = iter([1, 2, 10, 3, 6, 18, 5, 15])
+        iterable2 = process_iterable_helper(iterable1, in_predicate=predicate1,
+                                            out_predicate=predicate2, processor=processor)
+        self.assertIsInstance(iterable2, collections.abc.Iterable)
+        list2 = list(iterable2)
+        self.assertEqual(list2, [2, 6])
+
+
+class ProcessIterableHelperAsyncTest(unittest.TestCase):
+
+    @deferred_f_from_coro_f
+    async def test_async_in_predicate(self):
+        iterable1 = as_async_generator([1, 2, 3])
+        iterable2 = process_iterable_helper(iterable1, in_predicate=predicate1)
+        self.assertIsInstance(iterable2, collections.abc.AsyncIterable)
+        list2 = await collect_asyncgen(iterable2)
+        self.assertEqual(list2, [1, 3])
+
+    @deferred_f_from_coro_f
+    async def test_async_out_predicate(self):
+        iterable1 = as_async_generator([1, 2, 10, 3, 15])
+        iterable2 = process_iterable_helper(iterable1, out_predicate=predicate2)
+        self.assertIsInstance(iterable2, collections.abc.AsyncIterable)
+        list2 = await collect_asyncgen(iterable2)
+        self.assertEqual(list2, [1, 2, 3])
+
+    @deferred_f_from_coro_f
+    async def test_async_processor(self):
+        iterable1 = as_async_generator([1, 2, 3])
+        iterable2 = process_iterable_helper(iterable1, processor=processor)
+        self.assertIsInstance(iterable2, collections.abc.AsyncIterable)
+        list2 = await collect_asyncgen(iterable2)
+        self.assertEqual(list2, [2, 4, 6])
+
+    @deferred_f_from_coro_f
+    async def test_async_combined(self):
+        iterable1 = as_async_generator([1, 2, 10, 3, 6, 18, 5, 15])
+        iterable2 = process_iterable_helper(iterable1, in_predicate=predicate1,
+                                            out_predicate=predicate2, processor=processor)
+        self.assertIsInstance(iterable2, collections.abc.AsyncIterable)
+        list2 = await collect_asyncgen(iterable2)
+        self.assertEqual(list2, [2, 6])