Fix single frame GUI increment (#1254)

* Fix frame increment for single frame videos

* Add test and lint

sleap/gui/state.py

@@ -21,7 +21,7 @@
 """
 
 import inspect
-from typing import Any, Callable, List, Union
+from typing import Any, Callable, List, Union, Optional
 
 
 GSVarType = str
@@ -83,28 +83,31 @@ def toggle(self, key: GSVarType, default: bool = False):
         """Toggle boolean value for specified key."""
         self[key] = not self.get(key, default=default)
 
-    def increment(self, key: GSVarType, step: int = 1, mod: int = 1, default: int = 0):
+    def increment(
+        self, key: GSVarType, step: int = 1, mod: Optional[int] = None, default: int = 0
+    ):
         """Increment numeric value for specified key.
 
         Args:
             key: The key.
             step: What to add to current value.
-            mod: Wrap value (i.e., apply modulus) if not 1.
+            mod: Wrap value (i.e., apply modulus) if not None.
             default: Set value to this if there's no current value for key.
 
         Returns:
             None.
         """
         if key not in self._state_vars:
             self[key] = default
-        else:
-            new_value = self.get(key) + step
+            return
+
+        new_value = self.get(key) + step
 
-            # take modulo of value if mod arg is not 1
-            if mod != 1:
-                new_value %= mod
+        # Wrap the value if it's out of bounds.
+        if mod is not None:
+            new_value %= mod
 
-            self[key] = new_value
+        self[key] = new_value
 
     def increment_in_list(
         self, key: GSVarType, value_list: list, reverse: bool = False

tests/gui/test_state.py

@@ -50,9 +50,14 @@ def set_y_from_val_param_callback(x):
     assert times_x_changed == 4
     assert state["x"] == 2
 
+    # Test incrementing value with modulus of 1
+    state.increment("x", mod=1)
+    assert times_x_changed == 5
+    assert state["x"] == 0
+
     # test emitting callbacks without changing value
     state.emit("x")
-    assert times_x_changed == 5
+    assert times_x_changed == 6
 
 
 def test_gui_state_bool():