reports: Let RelatedPostings be initialized with an Iterable[Posting].

conservancy_beancount/reports/core.py

@@ -98,8 +98,8 @@ class RelatedPostings(Sequence[data.Posting]):
     for an example.
     """
 
-    def __init__(self) -> None:
-        self._postings: List[data.Posting] = []
+    def __init__(self, source: Iterable[data.Posting]=()) -> None:
+        self._postings: List[data.Posting] = list(source)
 
     @classmethod
     def group_by_meta(cls,

tests/test_reports_related_postings.py

@@ -63,6 +63,18 @@ def two_accruals_three_payments():
         (-550, 'EUR'),
     ))
 
+def test_initialize_with_list(credit_card_cycle):
+    related = core.RelatedPostings(credit_card_cycle[0].postings)
+    assert len(related) == 2
+
+def test_initialize_with_iterable(two_accruals_three_payments):
+    related = core.RelatedPostings(
+        post for txn in two_accruals_three_payments
+        for post in txn.postings
+        if post.account == 'Assets:Receivable:Accounts'
+    )
+    assert len(related) == 5
+
 def test_balance_empty():
     balance = core.RelatedPostings().balance()
     assert not balance
@@ -79,13 +91,21 @@ def test_balance_credit_card(credit_card_cycle):
         assert related.balance() == testutil.balance_map(USD=expected)
     assert expected == 0
 
-def test_clear():
+def test_clear_after_add():
     related = core.RelatedPostings()
     related.add(testutil.Posting('Income:Donations', -10))
     assert related.balance()
     related.clear()
     assert not related.balance()
 
+def test_clear_after_initialization():
+    related = core.RelatedPostings([
+        testutil.Posting('Income:Donations', -12),
+    ])
+    assert related.balance()
+    related.clear()
+    assert not related.balance()
+
 def check_iter_with_balance(entries):
     expect_posts = [txn.postings[0] for txn in entries]
     expect_balances = []