From 4870488324ed616aaea632194ee59283c9fa6bdd Mon Sep 17 00:00:00 2001
From: JoFrhwld <JoFrhwld@gmail.com>
Date: Fri, 3 Nov 2023 10:54:07 -0400
Subject: [PATCH] better exceptions for .first, .last

---
 src/aligned_textgrid/mixins/mixins.py  | 22 ++++++++++++----------
 tests/test_sequences/test_sequences.py | 19 +++++++++++++++++++
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/src/aligned_textgrid/mixins/mixins.py b/src/aligned_textgrid/mixins/mixins.py
index 5055397..cfdcd02 100644
--- a/src/aligned_textgrid/mixins/mixins.py
+++ b/src/aligned_textgrid/mixins/mixins.py
@@ -11,24 +11,26 @@ class PrecedenceMixins:
 
     Attributes:
         first (SequenceInterval): The first interval in the subset list
-        last  (SequenceInterval): The last interval in the subset list
+        last (SequenceInterval): The last interval in the subset list
     """
 
     @property
     def first(self):
-        if hasattr(self, "subset_list"):
+        if hasattr(self, "subset_list") and len(self.subset_list) > 0:
             return self.subset_list[0]
-        else:
-            raise Exception(f"{type(self).__name__} does not\
-                             have the attribute .first")
-        
+        if hasattr(self, "subset_list"):
+            raise IndexError(f"{type(self).__name__} with label "\
+                             f"'{self.label}' subset list is empty.")
+        raise AttributeError(f"{type(self).__name__} is not indexable.")
+                
     @property
     def last(self):
-        if hasattr(self, "subset_list"):
+        if hasattr(self, "subset_list") and len(self.subset_list) > 0:
             return self.subset_list[-1]
-        else:
-            raise Exception(f"{type(self).__name__} does not\
-                             have the attribute .first")        
+        if hasattr(self, "subset_list"):
+            raise IndexError(f"{type(self).__name__} with label "\
+                             f"'{self.label}' subset list is empty.")
+        raise AttributeError(f"{type(self).__name__} is not indexable.")        
 
     def set_fol(
             self, next_int):
diff --git a/tests/test_sequences/test_sequences.py b/tests/test_sequences/test_sequences.py
index 9737b4d..6ee2d90 100644
--- a/tests/test_sequences/test_sequences.py
+++ b/tests/test_sequences/test_sequences.py
@@ -1,8 +1,10 @@
 import pytest
 from aligned_textgrid.sequences.sequences import *
+from aligned_textgrid.points.points import SequencePoint
 from aligned_textgrid.sequences.tiers import *
 import numpy as np
 from praatio.utilities.constants import Interval
+from praatio.utilities.constants import Point
 
 class TestSequenceIntervalDefault:
     """_Test default behavior of SequenceInterval_
@@ -295,6 +297,23 @@ def test_first_last(self):
         last_interval = upper1[-1]
         assert upper1.last is last_interval
 
+    def test_first_last_errors(self):
+        upper1 = self.UpperClass(Interval(0,10,"upper"))
+        point1 = SequencePoint(Point(0, "point"))
+
+        with pytest.raises(IndexError):
+            upper1.first
+
+        with pytest.raises(IndexError):
+            upper1.last
+
+        with pytest.raises(AttributeError):
+            point1.first
+
+        with pytest.raises(AttributeError):
+            point1.last            
+
+
     def test_subset_pop(self):
         upper1 = self.UpperClass(Interval(0,10,"upper"))
         lower1 = self.LowerClass(Interval(0,5,"lower1"))