Renamed preserve to overwrite

Renamed the `preserve` property of `VariableAssignmentCommand` to
overwrite, changed its default to True, and reversed how it was used
that existing values are now preserved when it is not set.

src/dynamicprompts/commands/variable_commands.py

@@ -10,7 +10,7 @@ class VariableAssignmentCommand(Command):
     name: str
     value: Command
     immediate: bool
-    preserve: bool = False
+    overwrite: bool = True
     sampling_method = None
 
 

src/dynamicprompts/parser/parse.py

@@ -240,7 +240,7 @@ def _configure_variable_assignment(
         + OPT_WS
         + var_name("name")
         + OPT_WS
-        + pp.Opt(pp.Literal("?"))("preserve")
+        + pp.Opt(pp.Literal("?"))("preserve_existing_value")
         + pp.Literal("=")
         + pp.Opt(pp.Literal("!"))("immediate")
         + OPT_WS
@@ -402,7 +402,7 @@ def _parse_variable_assignment_command(
     return VariableAssignmentCommand(
         name=parts["name"],
         value=parts["value"],
-        preserve=("preserve" in parts),
+        overwrite=("preserve_existing_value" not in parts),
         immediate=("immediate" in parts),
     )
 

src/dynamicprompts/sampling_context.py

@@ -162,7 +162,7 @@ def process_variable_assignment(
         self,
         command: VariableAssignmentCommand,
     ) -> Command:
-        if command.preserve and command.name in self.variables:
+        if not command.overwrite and command.name in self.variables:
             return self.variables[command.name]
         if command.immediate:
             if isinstance(command.value, LiteralCommand):

tests/parser/test_parser.py

@@ -390,17 +390,14 @@ def test_alternative_wildcard_wrap(self, wildcard_wrap: str, template: str):
         assert variant.values[1].literal == "B"
         assert variant.values[2].wildcard == "some/wildcard"
 
+    @pytest.mark.parametrize("immediate", (False, True), ids=("delayed", "immediate"))
     @pytest.mark.parametrize(
-        ("immediate", "preserve"),
-        [
-            (False, False),
-            (False, True),
-            (True, False),
-            (True, True),
-        ],
+        "overwrite",
+        (False, True),
+        ids=("preserve existing value", "overwrite existing value"),
     )
-    def test_variable_commands(self, immediate: bool, preserve: bool):
-        op = "?" if preserve else ""
+    def test_variable_commands(self, immediate: bool, overwrite: bool):
+        op = "?" if not overwrite else ""
         op += "=!" if immediate else "="
         sequence = cast(
             SequenceCommand,
@@ -411,7 +408,7 @@ def test_variable_commands(self, immediate: bool, preserve: bool):
         assert isinstance(ass, VariableAssignmentCommand)
         assert ass.name == "animal"
         assert ass.value == LiteralCommand("cat")
-        assert ass.preserve == preserve
+        assert ass.overwrite == overwrite
         assert ass.immediate == immediate
         acc = sequence[2]
         assert isinstance(acc, VariableAccessCommand)