namespaces.ipynb

{
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  {
   "metadata": {},
   "cell_type": "markdown",
   "source": "# Multiple namespaces for IPython\n\n<blockquote class=\"twitter-tweet\" data-partner=\"tweetdeck\"><p lang=\"en\" dir=\"ltr\">Feature request for <a href=\"https://twitter.com/ProjectJupyter\">@ProjectJupyter</a>: Define multiple namespaces within the same notebook (without using functions).</p>&mdash; Juan Manuel Caicedo (@cavorite) <a href=\"https://twitter.com/cavorite/status/728354406723297281\">May 5, 2016</a></blockquote>\n<script async src=\"//platform.twitter.com/widgets.js\" charset=\"utf-8\"></script>\n\nThis is a simple proof-of-concept implementation of switching namespaces via magics. The key points we need:\n\n1. IPython's namespace is stored on the `.user_ns` attribute on the IPython instance\n2. IPython relies on some globals in the user ns created with `ip.init_user_ns`\n3. A namespace in Python is a dict\n\n"
  },
  {
   "metadata": {},
   "cell_type": "markdown",
   "source": "First, we create a dict of namespaces by name on IPython, and save the initial value:"
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": true
   },
   "cell_type": "code",
   "source": "ip = get_ipython()\nip.namespaces = {}\nip._original_user_ns = ip.user_ns",
   "execution_count": 1,
   "outputs": []
  },
  {
   "metadata": {},
   "cell_type": "markdown",
   "source": "Next, we define a `%ns` line magic for switching namespaces by name:\n\nWe use ChainMap so that globals that IPython defines, such as In, Out, etc. are available no matter what namespace we switch to:"
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "from collections import ChainMap\n\ndef set_namespace(name):\n    \"\"\"Line magic for switching namespaces:\n    \n    %ns foo\n    a = 5\n\n    %ns bar\n    a = 10\n\n    %ns foo\n    print(a)\n    # 10\n    \"\"\"\n    if name not in ip.namespaces:\n        ip.namespaces[name] = ChainMap({}, ip._original_user_ns)\n    ip.user_ns = ip.namespaces[name]\n\nip.register_magic_function(set_namespace, magic_name='ns')\nset_namespace('default')",
   "execution_count": 2,
   "outputs": []
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "%ns foo\n\na = 5\n\n%ns bar\n\na = 10\n\n%ns foo\n\na",
   "execution_count": 3,
   "outputs": [
    {
     "metadata": {},
     "data": {
      "text/plain": "5"
     },
     "execution_count": 3,
     "output_type": "execute_result"
    }
   ]
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "ip.namespaces['foo']['a']",
   "execution_count": 4,
   "outputs": [
    {
     "metadata": {},
     "data": {
      "text/plain": "5"
     },
     "execution_count": 4,
     "output_type": "execute_result"
    }
   ]
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "ip.namespaces['bar']['a']",
   "execution_count": 5,
   "outputs": [
    {
     "metadata": {},
     "data": {
      "text/plain": "10"
     },
     "execution_count": 5,
     "output_type": "execute_result"
    }
   ]
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "%whos",
   "execution_count": 6,
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": "Variable        Type        Data/Info\n-------------------------------------\nChainMap        ABCMeta     <class 'collections.ChainMap'>\na               int         5\nset_namespace   function    <function set_namespace at 0x109866d90>\n"
    }
   ]
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "%ns bar\n%whos",
   "execution_count": 7,
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": "Variable        Type        Data/Info\n-------------------------------------\nChainMap        ABCMeta     <class 'collections.ChainMap'>\na               int         10\nset_namespace   function    <function set_namespace at 0x109866d90>\n"
    }
   ]
  },
  {
   "metadata": {},
   "cell_type": "markdown",
   "source": "We can also make a cell magic for running a whole cell in a given namespace,\nthen switching back to whatever was already active:"
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": true
   },
   "cell_type": "code",
   "source": "def namespace_cell(name, cell):\n    \"\"\"Cell magic for running a single cell in a given namespace\n    \n    %%ns foo\n    a = 5\n    \"\"\"\n    save_ns = ip.user_ns\n    set_namespace(name)\n    try:\n        ip.run_cell(cell)\n    finally:\n        ip.user_ns = save_ns\n    \n    \nip.register_magic_function(namespace_cell, magic_kind='cell', magic_name='ns')",
   "execution_count": 8,
   "outputs": []
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "%%ns cellns\n\na = 'hello,'\nprint(a * 2)",
   "execution_count": 9,
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": "hello,hello,\n"
    }
   ]
  },
  {
   "metadata": {},
   "cell_type": "markdown",
   "source": "This didn't affect the running namespace:"
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "a",
   "execution_count": 10,
   "outputs": [
    {
     "metadata": {},
     "data": {
      "text/plain": "10"
     },
     "execution_count": 10,
     "output_type": "execute_result"
    }
   ]
  },
  {
   "metadata": {},
   "cell_type": "markdown",
   "source": "But we can recall the cell namespace:"
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "%%ns cellns\na",
   "execution_count": 11,
   "outputs": [
    {
     "metadata": {},
     "data": {
      "text/plain": "'hello,'"
     },
     "execution_count": 11,
     "output_type": "execute_result"
    }
   ]
  },
  {
   "metadata": {
    "trusted": true,
    "collapsed": false
   },
   "cell_type": "code",
   "source": "for name, ns in ip.namespaces.items():\n    print(name, ns.get('a', 'undefined'))",
   "execution_count": 12,
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": "foo 5\nbar 10\ndefault undefined\ncellns hello,\n"
    }
   ]
  }
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