filters: Add iter_unique() function.

conservancy_beancount/filters.py

@@ -24,9 +24,13 @@ from . import rtutil
 
 from typing import (
     cast,
+    Hashable,
     Iterable,
+    Iterator,
     Optional,
     Pattern,
+    Set,
+    TypeVar,
     Union,
 )
 from .beancount_types import (
@@ -37,6 +41,8 @@ from .beancount_types import (
     Transaction,
 )
 
+# Saying Optional works around <https://github.com/python/mypy/issues/8768>.
+HashT = TypeVar('HashT', bound=Optional[Hashable])
 Postings = Iterable[data.Posting]
 Regexp = Union[str, Pattern]
 
@@ -72,6 +78,13 @@ def filter_for_rt_id(postings: Postings, ticket_id: Union[int, str]) -> Postings
     regexp = rtutil.RT.metadata_regexp(ticket_id, first_link_only=True)
     return filter_meta_match(postings, 'rt-id', regexp)
 
+def iter_unique(seq: Iterable[HashT]) -> Iterator[HashT]:
+    seen: Set[HashT] = set()
+    for item in seq:
+        if item not in seen:
+            seen.add(item)
+            yield item
+
 def remove_opening_balance_txn(entries: Entries) -> Optional[Transaction]:
     """Remove an opening balance transaction from entries returned by Beancount
 

conservancy_beancount/reports/accrual.py

@@ -207,17 +207,11 @@ class AccrualPostings(core.RelatedPostings):
         return item1 if all_same else self.INCONSISTENT
 
     def entities(self, pred: Callable[[data.Posting], bool]=bool) -> Iterator[MetaValue]:
-        seen: Set[MetaValue] = set()
-        for post in self:
-            if pred(post):
-                try:
-                    entity = post.meta['entity']
-                except KeyError:
-                    pass
-                else:
-                    if entity not in seen:
-                        yield entity
-                        seen.add(entity)
+        return filters.iter_unique(
+            post.meta['entity']
+            for post in self
+            if pred(post) and 'entity' in post.meta
+        )
 
     def first_links(self, key: MetaKey, default: Optional[str]=None) -> Iterator[Optional[str]]:
         return (post.meta.first_link(key, default) for post in self)

tests/test_filters.py

@@ -183,3 +183,6 @@ def test_audit_date(entry):
         assert actual is None
     else:
         assert actual == entry.date
+
+def test_iter_unique():
+    assert list(filters.iter_unique('1213231')) == list('123')