first_last for tiers

src/aligned_textgrid/mixins/tiermixins.py

@@ -3,7 +3,28 @@ class TierMixins:
 
     Attributes:
         []: indexable and iterable
+        first (SequenceInterval): The first entry in the tier.
+        last (SequenceInterval): The last entry in the tier.
     """
+
+    @property
+    def first(self):
+        if hasattr(self, "sequence_list") and len(self.sequence_list) > 0:
+            return self.sequence_list[0]
+        if hasattr(self, "sequence_list"):
+            raise IndexError(f"{type(self).__name__} tier with name"\
+                             f" {self.name} has empty sequence_list")
+        raise AttributeError(f"{type(self).__name__} is not indexible.")
+
+    @property
+    def last(self):
+        if hasattr(self, "sequence_list") and len(self.sequence_list) > 0:
+            return self.sequence_list[-1]
+        if hasattr(self, "sequence_list"):
+            raise IndexError(f"{type(self).__name__} tier with name"\
+                             f" {self.name} has empty sequence_list")
+        raise AttributeError(f"{type(self).__name__} is not indexible.")
+
     def __contains__(self, item):
         return item in self.sequence_list
 

tests/test_tiers/test_PointTier.py

@@ -58,6 +58,28 @@ def test_return(self):
         out_tier = self.seq_point_tier.return_tier()
         assert isinstance(out_tier, PointTier)
 
+class TestPointPrecedence:
+    def test_first_last(self):
+        point_a = SequencePoint(Point(1, "a"))
+        point_b = SequencePoint(Point(2, "b"))
+        point_c = SequencePoint(Point(3, "c"))
+
+        tier = SequencePointTier(tier = [point_a, point_b, point_c])
+
+        first_point = tier[0]
+        assert tier.first is first_point
+
+        last_point = tier[-1]
+        assert tier.last is last_point
+
+    def test_first_last_error(self):
+        tier = SequencePointTier()
+
+        with pytest.raises(IndexError):
+            tier.first
+
+
+
 class TestPointGroup:
     point_a = Point(1, "a")
     point_b = Point(2, "b")

tests/test_tiers/test_SequenceTier.py

@@ -212,6 +212,27 @@ def test_sequence_index(self):
         for idx, entry in enumerate(tier):
             assert entry.tier_index == idx
 
+    def test_first_last(self):
+        tier = SequenceTier(
+            tier = [
+                self.interval1,
+                self.interval2,
+                self.interval3
+                ]
+            )
+
+        first_interval = tier[0]
+        assert tier.first is first_interval
+
+        last_interval = tier[-1]
+        assert tier.last is last_interval
+
+    def test_first_last_errors(self):
+        tier = SequenceTier()
+
+        with pytest.raises(IndexError):
+            tier.first
+
     def test_get_tieridx(self):
         tier = SequenceTier(
             tier = [