Fix negative indices for __setitem__ in StringList

Author: domdfcoding

domdf_python_tools/stringlist.py

@@ -228,6 +228,8 @@ def __setitem__(self, index: Union[int, slice], line: Union[String, Iterable[Str
 		if isinstance(index, int):
 			if self and index < len(self):
 				self.pop(index)
+			if index < 0:
+				index = len(self) + index + 1
 			self.insert(index, line)
 
 		elif isinstance(index, slice):

tests/test_stringlist.py

@@ -118,6 +118,17 @@ def test_start_of_line_indents(self):
 		assert StringList("Hello\n    World") == ["Hello", "    World"]
 		assert StringList("Hello\n    World", convert_indents=True) == ["Hello", "\tWorld"]
 
+	def test_negative_getitem(self):
+		sl = StringList(['', '', "hello", "world", '', '', 'abc', "1234"])
+
+		assert sl[-1] == "1234"
+		sl[-1] += "5678"
+		assert sl == ['', '', "hello", "world", '', '', 'abc', "12345678"]
+
+		assert sl[-2] == "abc"
+		sl[-2] += "def"
+		assert sl == ['', '', "hello", "world", '', '', 'abcdef', "12345678"]
+
 	def test_indent_size(self):
 		sl = StringList(['', '', "hello", "world", '', '', '', "1234"])