Add __bool__ method to TimeStamp and TimeSpan classes

fastkml/times.py

@@ -164,6 +164,10 @@ def __init__(
         super().__init__(ns=ns, name_spaces=name_spaces, id=id, target_id=target_id)
         self.timestamp = timestamp
 
+    def __bool__(self) -> bool:
+        """Return True if the timestamp is valid."""
+        return bool(self.timestamp)
+
     def etree_element(
         self,
         precision: Optional[int] = None,
@@ -214,6 +218,10 @@ def __init__(
         self.begin = begin
         self.end = end
 
+    def __bool__(self) -> bool:
+        """Return True if the begin or end date is valid."""
+        return bool(self.begin) or bool(self.end)
+
     def etree_element(
         self,
         precision: Optional[int] = None,
@@ -234,10 +242,6 @@ def etree_element(
                     f"{self.ns}end",
                 )
                 end.text = text
-        if self.begin == self.end is None:
-            msg = "Either begin, end or both must be set"
-            raise ValueError(msg)
-        # TODO test if end > begin
         return element
 
     @classmethod

tests/times_test.py

@@ -219,8 +219,9 @@ def test_timespan(self) -> None:
         ts.end = None
         assert now.dt.isoformat() not in str(ts.to_string())
         assert y2k.dt.isoformat() in str(ts.to_string())
+        assert ts
         ts.begin = None
-        pytest.raises(ValueError, ts.to_string)
+        assert not ts
 
     def test_feature_timestamp(self) -> None:
         now = datetime.datetime.now()