core: improvements for warnings, twitter/rss: try using @warn_if_empty

my/rss/all.py

@@ -1,11 +1,16 @@
 '''
 Unified RSS data, merged from different services I used historically
 '''
+# NOTE: you can comment out the sources you're not using
+from . import feedbin, feedly
+
 from typing import Iterable
 from .common import Subscription, compute_subscriptions
 
 
 def subscriptions() -> Iterable[Subscription]:
-    from . import feedbin, feedly
     # TODO google reader?
-    yield from compute_subscriptions(feedbin.states(), feedly.states())
+    yield from compute_subscriptions(
+        feedbin.states(),
+        feedly .states(),
+    )

my/rss/common.py

@@ -17,6 +17,8 @@ from typing import Iterable, Tuple, Sequence
 SubscriptionState = Tuple[datetime, Sequence[Subscription]]
 
 
+from ..core import warn_if_empty
+@warn_if_empty
 def compute_subscriptions(*sources: Iterable[SubscriptionState]) -> List[Subscription]:
     """
     Keeps track of everything I ever subscribed to.
@@ -34,6 +36,9 @@ def compute_subscriptions(*sources: Iterable[SubscriptionState]) -> List[Subscri
             if feed.url not in by_url:
                 by_url[feed.url] = feed
 
+    if len(states) == 0:
+        return []
+
     _, last_state = max(states, key=lambda x: x[0])
     last_urls = {f.url for f in last_state}