Support for an initial before_attribute in stream_generator

AUTHORS.rst

@@ -84,4 +84,5 @@ Source Contributors
 - Josh Kim `@jsk56143 <https://github.com/jsk56143>`_
 - Rolf Campbell `@endlisnis <https://github.com/endlisnis>`_
 - zacc `@zacc <https://github.com/zacc>`_
+- c0d3rman `@c0d3rman <https://github.com/c0d3rman>`
 - Add "Name <email (optional)> and github profile link" above this line.

praw/models/util.py

@@ -35,7 +35,12 @@ def permissions_string(
 
 
 @_deprecate_args(
-    "function", "pause_after", "skip_existing", "attribute_name", "exclude_before"
+    "function",
+    "pause_after",
+    "skip_existing",
+    "attribute_name",
+    "exclude_before",
+    "start_after",
 )
 def stream_generator(
     function: Callable,
@@ -44,6 +49,7 @@ def stream_generator(
     exclude_before: bool = False,
     pause_after: int | None = None,
     skip_existing: bool = False,
+    start_after: str | None = None,
     **function_kwargs: Any,
 ) -> Generator[Any, None, None]:
     """Yield new items from ``function`` as they become available.
@@ -62,6 +68,8 @@ def stream_generator(
     :param skip_existing: When ``True``, this does not yield any results from the first
         request thereby skipping any items that existed in the stream prior to starting
         the stream (default: ``False``).
+    :param start_after: The initial string value to use for ``before`` in ``params``.
+        The stream will start from the item following this one (default: ``None``).
 
     Additional keyword arguments will be passed to ``function``.
 
@@ -122,7 +130,7 @@ def stream_generator(
             print(comment)
 
     """
-    before_attribute = None
+    before_attribute = start_after
     exponential_counter = ExponentialCounter(max_counter=16)
     seen_attributes = BoundedSet(301)
     without_before_counter = 0

tests/integration/models/reddit/test_subreddit.py

@@ -954,6 +954,16 @@ def test_comments__with_skip_existing(self, reddit):
         # that there are at least 400 comments in the stream.
         assert count < 400
 
+    def test_comments__with_start_after(self, reddit):
+        subreddit = reddit.subreddit("kakapo")
+        initial_stream = subreddit.stream.comments()
+        first_ten = [next(initial_stream) for _ in range(10)]
+        generator = subreddit.stream.comments(start_after=first_ten[4].fullname)
+        for i in range(5):
+            comment = next(generator)
+            assert isinstance(comment, Comment)
+            assert comment.fullname == first_ten[i + 5].fullname
+
     def test_submissions(self, reddit):
         subreddit = reddit.subreddit("all")
         generator = subreddit.stream.submissions()

tests/unit/models/test_util.py

@@ -124,3 +124,33 @@ def generate(limit, **kwargs):
             thing = next(stream)
             assert thing not in seen
             seen.add(thing)
+
+    def test_stream_start_after(
+        self,
+    ):
+        Thing = namedtuple("Thing", ["fullname"])
+        initial_things = [Thing(n) for n in reversed(range(100))]
+        counter = 99
+
+        def generate(limit, params=None, **kwargs):
+            nonlocal counter
+            counter += 1
+            sliced_things = initial_things
+            if params:
+                sliced_things = initial_things[
+                    : next(
+                        i
+                        for i, thing in enumerate(initial_things)
+                        if thing.fullname == params["before"]
+                    )
+                ]
+            if counter % 2 == 0:
+                return sliced_things
+            return [Thing(counter)] + sliced_things[:-1]
+
+        stream = stream_generator(generate, start_after=49)
+        expected_fullname = 50
+        for _ in range(50):
+            thing = next(stream)
+            assert thing.fullname == expected_fullname, thing
+            expected_fullname += 1