Traitlets early experiments

Traitlets.ipynb

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  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "outputs": [],
   "source": [
    "import sys; print(sys.version)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "import traitlets\n",
    "print(\"traitlets\", traitlets.__version__, traitlets.__file__)\n",
    "from traitlets import HasTraits, Int, Float, Unicode, observe, Any, All\n",
    "import time"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "source": [
    "class MyClass(HasTraits):\n",
    "    i = Int()\n",
    "    f = Float()\n",
    "    u = Unicode()\n",
    "\n",
    "mc1 = MyClass()\n",
    "mc1.i = 42"
   ]
  },
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   "cell_type": "code",
   "execution_count": null,
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   },
   "outputs": [],
   "source": [
    "try:\n",
    "    mc1.i = \"33\"\n",
    "except Exception as e:\n",
    "    print(type(e))\n",
    "    print(e)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
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   "outputs": [],
   "source": [
    "class MyClass(HasTraits):\n",
    "    i = Int()\n",
    "    f = Float()\n",
    "    u = Unicode()\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "    @observe(All)\n",
    "    def _class_observed_changed(self, c):\n",
    "        print(\"class observed obj {}.{} was {!r} is now {!r}\".format(self.name, c.name, c.old, c.new), sep='\\n')\n",
    "        c[\"timestamp\"] = time.asctime(time.localtime())\n",
    "\n",
    "mc1 = MyClass('mc1')\n",
    "mc1.i = 42\n",
    "mc1.f = 3.14159\n",
    "mc1.u = \"Python Programming\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "def report_change(c):\n",
    "    print(\"R_C: {}.{} was {!r} is now {!r}\".format(c.owner.name, c.name, c.old, c.new))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "mc1.observe(report_change) # reports all trait changes on instance"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "mc1.i = 102 # Now reported by both class and instance"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "mc1.f = 3.2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "mc1.u = \"the quick brown fox\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "mc2 = MyClass('mc2')\n",
    "def _mc_changed(c):\n",
    "    print(\"{}.{} changed\".format(c.owner.name, c.name))\n",
    "#mc2.observe(report_change)\n",
    "mc2.observe(_mc_changed, [\"i\", \"f\"]) #  # reports selected trait changes on instance\n",
    "\n",
    "print(\"-- i changes --\")\n",
    "mc2.i = 101\n",
    "print(\"-- f changes --\")\n",
    "mc2.f = 1.234\n",
    "print(\"-- u changes --\")\n",
    "mc2.u =  \"Steve Holden\" # still gets class notification and report change"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "def _mc_changed(c):\n",
    "    print(\"instance changed\", c.name, \"to\", c.new)\n",
    "mc1.observe(_mc_changed, [\"i\", \"f\"]) # reports changes only to mc2.i and mc2.f\n",
    "\n",
    "print(\"-- mc1.i changes --\")\n",
    "mc1.i = 1001\n",
    "print(\"-- mc1.f changes --\")\n",
    "mc1.f = 1.543219\n",
    "print(\"-- mc1.u changes --\")\n",
    "mc1.u =  \"Sydney Poitier!\" # still gets class notification and report change\n",
    "print(\"-- mc2.i changes --\")\n",
    "mc2.i = 999\n",
    "print(\"-- mc2.f changes --\")\n",
    "mc2.f = 3.14159\n",
    "print(\"-- mc2.u changes --\")\n",
    "mc2.u = \"Somebody\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "So, here's a question.\n",
    "If you repeat the execution of the cell above, there are no notifications.\n",
    "Why this different output?\n",
    "\n",
    "Here's another one.\n",
    "If you change the values being bound to the traits and then execute the cell a _third_ time,\n",
    "why do you see the repeated notifications?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "mc2 = MyClass()\n",
    "mc2.observe(lambda c: (c.old, c.new))\n",
    "with mc1.hold_trait_notifications():\n",
    "    mc1.i = 1\n",
    "    mc2.i = 101\n",
    "    print(\"Releasing notification hold\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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