Stateful example

Author: jph00

fastcore/__init__.py

@@ -1 +1 @@
-__version__ = "1.3.5"
+__version__ = "1.3.6"

fastcore/basics.py

@@ -667,7 +667,7 @@ class Stateful:
     _stateattrs=()
     def __init__(self,*args,**kwargs):
         self._init_state()
-        super().__init__(*args,**kwargs)
+        super().__init__(*args,**kwargs) # required for mixin usage
 
     def __getstate__(self):
         return {k:v for k,v in self.__dict__.items()
@@ -678,7 +678,7 @@ def __setstate__(self, state):
         self._init_state()
 
     def _init_state(self):
-        "Override for custom deserialization logic"
+        "Override for custom init and deserialization logic"
         self._state = {}
 
 # Cell

nbs/01_basics.ipynb

@@ -3543,7 +3543,7 @@
     "    _stateattrs=()\n",
     "    def __init__(self,*args,**kwargs):\n",
     "        self._init_state()\n",
-    "        super().__init__(*args,**kwargs)\n",
+    "        super().__init__(*args,**kwargs) # required for mixin usage\n",
     "    \n",
     "    def __getstate__(self):\n",
     "        return {k:v for k,v in self.__dict__.items()\n",
@@ -3554,7 +3554,7 @@
     "        self._init_state()\n",
     "\n",
     "    def _init_state(self):\n",
-    "        \"Override for custom deserialization logic\"\n",
+    "        \"Override for custom init and deserialization logic\"\n",
     "        self._state = {}"
    ]
   },
@@ -3604,6 +3604,60 @@
     "test_eq(t2._state,{})"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Override `_init_state` to do any necessary setup steps that are required during `__init__` or during deserialization (e.g. `pickle.load`). Here's an example of how `Stateful` simplifies the official Python example for [Handling Stateful Objects](https://docs.python.org/3/library/pickle.html#handling-stateful-objects)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class TextReader(Stateful):\n",
+    "    \"\"\"Print and number lines in a text file.\"\"\"\n",
+    "    _stateattrs=('file',)\n",
+    "    def __init__(self, filename):\n",
+    "        self.filename,self.lineno = filename,0\n",
+    "        super().__init__()\n",
+    "\n",
+    "    def readline(self):\n",
+    "        self.lineno += 1\n",
+    "        line = self.file.readline()\n",
+    "        if line: return f\"{self.lineno}: {line.strip()}\"\n",
+    "\n",
+    "    def _init_state(self):\n",
+    "        self.file = open(self.filename)\n",
+    "        for _ in range(self.lineno): self.file.readline()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "1: {\n",
+      "2: \"cells\": [\n",
+      "3: {\n"
+     ]
+    }
+   ],
+   "source": [
+    "reader = TextReader(\"00_test.ipynb\")\n",
+    "print(reader.readline())\n",
+    "print(reader.readline())\n",
+    "\n",
+    "new_reader = pickle.loads(pickle.dumps(reader))\n",
+    "print(reader.readline())"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,

settings.ini

@@ -7,7 +7,7 @@ author = Jeremy Howard and Sylvain Gugger
 author_email = [email protected]
 copyright = fast.ai
 branch = master
-version = 1.3.5
+version = 1.3.6
 min_python = 3.6
 audience = Developers
 language = English