model: Move random seed and random to __init__ (#1940)

* model: Move random seed and random to __init__

Given that `super().__init__()` is now necessary for user's model class `__init__()`, this simplifies the `Model` construct.
And  `model.random` can be initialized with other RNG objects (`np.random.default_rng(...)`, or any other RNG).

Prior discussion #1938 Please enter the commit message for your changes. Lines starting

* model: Set seed as keyword argument

* make_model: Set seed after model initialization

This is because the seed param is no longer always passed by the user to
mesa.Model.__init__.

* add super call in model.__init__

* attempted debug

* Update test_time.py

* Update test_time.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Ensure object.__init__ has no other argument

* fix: Remove need of __new__ in ModelCreator

* Remove obsolete attributes

* Remove superfluous code

---------

Co-authored-by: Jan Kwakkel <j.h.kwakkel@tudelft.nl>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

mesa/model.py

@@ -54,29 +54,24 @@ class Model:
 
     """
 
-    def __new__(cls, *args: Any, **kwargs: Any) -> Any:
-        """Create a new model object and instantiate its RNG automatically."""
-        obj = object.__new__(cls)
-        obj._seed = kwargs.get("seed")
-        if obj._seed is None:
-            # We explicitly specify the seed here so that we know its value in
-            # advance.
-            obj._seed = random.random()
-        obj.random = random.Random(obj._seed)
-        return obj
-
-    def __init__(self, *args: Any, **kwargs: Any) -> None:
+    def __init__(self, *args: Any, seed: float | None = None, **kwargs: Any) -> None:
         """Create a new model. Overload this method with the actual code to
         start the model. Always start with super().__init__() to initialize the
         model object properly.
         """
-
         self.running = True
         self.schedule = None
         self.steps: int = 0
 
         self._setup_agent_registration()
 
+        self._seed = seed
+        if self._seed is None:
+            # We explicitly specify the seed here so that we know its value in
+            # advance.
+            self._seed = random.random()
+        self.random = random.Random(self._seed)
+
         # Wrap the user-defined step method
         self._user_step = self.step
         self.step = self._wrapped_step

mesa/visualization/solara_viz.py

@@ -260,10 +260,8 @@ def on_change(name, value):
         set_model_parameters({**model_parameters, name: value})
 
     def create_model():
-        model.value = model.value.__class__.__new__(
-            model.value.__class__, **model_parameters, seed=reactive_seed.value
-        )
-        model.value.__init__(**model_parameters)
+        model.value = model.value.__class__(**model_parameters)
+        model.value._seed = reactive_seed.value
 
     solara.use_effect(create_model, [model_parameters, reactive_seed.value])
 

tests/test_solara_viz.py

@@ -89,7 +89,6 @@ def test_call_space_drawer(mocker):
     )
 
     model = mesa.Model()
-    mocker.patch.object(mesa.Model, "__new__", return_value=model)
     mocker.patch.object(mesa.Model, "__init__", return_value=None)
 
     agent_portrayal = {

tests/test_time.py

@@ -5,7 +5,8 @@
 import unittest
 from unittest import TestCase, mock
 
-from mesa import Agent, Model
+from mesa.agent import Agent
+from mesa.model import Model
 from mesa.time import (
     BaseScheduler,
     RandomActivation,
@@ -111,6 +112,7 @@ def test_no_shuffle(self):
         """
         Testing the staged activation without shuffling.
         """
+
         model = MockModel(shuffle=False)
         model.step()
         model.step()