feat(picker): support negative default_index

src/pick/__init__.py

@@ -66,8 +66,11 @@ def __post_init__(self) -> None:
         if len(self.options) == 0:
             raise ValueError("options should not be an empty list")
 
-        if self.default_index >= len(self.options):
-            raise ValueError("default_index should be less than the length of options")
+        if self.default_index < -len(self.options) or self.default_index >= len(self.options):
+            raise ValueError("default_index is out of range of options")
+
+        if self.default_index < 0:
+            self.default_index += len(self.options)
 
         if self.multiselect and self.min_selection_count > len(self.options):
             raise ValueError(

tests/test_pick.py

@@ -1,4 +1,6 @@
-from pick import Picker, Option
+import pytest
+
+from pick import Option, Picker
 
 
 def test_move_up_down():
@@ -78,6 +80,21 @@ def test_disabled_option():
     picker.move_down()
     assert picker.get_selected() == (Option("option3"), 2)
 
+def test_negative_default_index():
+    options = ["option1", "option2", "option3"]
+    picker = Picker(options, default_index=-1)
+    assert picker.get_selected() == ("option3", 2)
+    lines, _ = picker.get_lines()
+    assert "* option3" in lines
+
+    picker = Picker(options, default_index=-3)
+    assert picker.get_selected() == ("option1", 0)
+
+    with pytest.raises(ValueError):
+        Picker(options, default_index=-4)
+    with pytest.raises(ValueError):
+        Picker(options, default_index=3)
+
 
 def test_mark_index_disabled_option():
     options = [Option("option1"), Option("option2", enabled=False), Option("option3")]