Add section on default values

Author: gjbex

source-code/pydantic.ipynb

@@ -10,7 +10,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 35,
+   "execution_count": 1,
    "id": "b2ba87d0-2447-4a4d-9bae-eb0e86d39ce1",
    "metadata": {},
    "outputs": [],
@@ -239,6 +239,136 @@
     "As you can see, a Python `dataclass` will not perform validation out-of-the-box."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "f9d4e8b1-22b7-4c25-adc0-fb8eb46ed26f",
+   "metadata": {},
+   "source": [
+    "## Default values"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "3b808ae6-0b73-4fb7-b570-593243b15448",
+   "metadata": {},
+   "source": [
+    "Attributes can have default values.  For types such as `int` or `str` these are simple constants for non-trivial types you can use `default_factory`."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "e00b9f60-5be3-4cea-9dcd-02497911c33e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class Agent(BaseModel):\n",
+    "    name: str\n",
+    "    interactive: bool = False\n",
+    "    tools: list[str] = Field(default_factory=list)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "98381d5a-c8ae-4c70-958d-43206747766c",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "agent1 = Agent(name='my_agent')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "c664f054-64fc-4a35-8cd6-77f9429313d4",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "False"
+      ]
+     },
+     "execution_count": 5,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "agent1.interactive"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "f031bf63-9de5-4c96-b153-e510da32f223",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "[]"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "agent1.tools"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "61bf4564-9266-4edd-a55a-3d796daeffa9",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "agent1.tools.append('screwdriver')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "e5b860c1-530b-4cf7-8e79-30806039ce35",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "agent2 = Agent(name='my_other_agent')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "edfcebbe-5a7d-4c1c-b47a-2d8c3ddd54f3",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "[]"
+      ]
+     },
+     "execution_count": 10,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "agent2.tools"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "094eb08a-1ae8-4d42-9c18-d635ea3fca70",
+   "metadata": {},
+   "source": [
+    "It is clear that using `default_factory` results in the right behavior."
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "c31de1d8-2744-48b7-9914-bfeb90cfdac0",
@@ -608,7 +738,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.12.7"
+   "version": "3.12.3"
   }
  },
  "nbformat": 4,