Experiment with dictionaries that allow for some kind of references between its keys. Think of somehing like a poor man's version of references in [HOCON](https://en.wikipedia.org/wiki/HOCON).

test_ref_dicts.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Test dictionaries with internal references\n",
    "\n",
    "Experiment with dictionaries that allow for some kind of references between its keys. Think of somehing like a poor man's version of references in [HOCON](https://en.wikipedia.org/wiki/HOCON)."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'foo' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-1-04a43d9d99f9>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      2\u001b[0m config = dict(\n\u001b[1;32m      3\u001b[0m     \u001b[0mfoo\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m\"FOO\"\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 4\u001b[0;31m     \u001b[0mbar\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34mf\"{foo}bar\"\u001b[0m \u001b[0;31m# should evaluate to \"FOObar\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      5\u001b[0m )\n",
      "\u001b[0;31mNameError\u001b[0m: name 'foo' is not defined"
     ]
    }
   ],
   "source": [
    "# We want references like this to work (a bit like in HOCON):\n",
    "config = dict(\n",
    "    foo = \"FOO\",\n",
    "    bar = f\"{foo}bar\" # should evaluate to \"FOObar\"\n",
    ")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Experimental implementation"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Define a dictionary class with references that should be good enough for basic datastructures like those in JSON. This does not treat custom data types. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "from collections import OrderedDict\n",
    "\n",
    "class RefOrderedDict(OrderedDict):\n",
    "    \"An ordered dict with strings able to reference other internal keys.\"\n",
    "\n",
    "    def resolve_refs(self, v):\n",
    "        deref = self.resolve_refs\n",
    "        typ = type(v)\n",
    "        if typ == str:\n",
    "            return eval('f' + repr(v), None, self)\n",
    "        elif typ == list:\n",
    "            return [deref(el) for el in v]\n",
    "        elif typ == set:\n",
    "            return {deref(el) for el in v}\n",
    "        elif typ == dict:\n",
    "            return {deref(el): deref(v[el]) for el in v}\n",
    "        else:\n",
    "            return v\n",
    "\n",
    "    def __setitem__(self, k, v):\n",
    "        v = self.resolve_refs(v)\n",
    "        super().__setitem__(k, v)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Some test cases"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "OrderedDict([('foo', 'FOO'), ('bar', '{foo}bar')])"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "OrderedDict(foo=\"FOO\", bar=\"{foo}bar\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "RefOrderedDict([('foo', 'FOO'), ('bar', 'FOObar')])"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "RefOrderedDict(foo=\"FOO\", bar=\"{foo}bar\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "RefOrderedDict([('x', '42'), ('y', 'ref to x: 42'), (1, 2)])\n"
     ]
    }
   ],
   "source": [
    "d = RefOrderedDict(x='42', y='ref to x: {x}')\n",
    "d[1] = 2\n",
    "print(d)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "RefOrderedDict([('foo', 'FOO'), ('bar', [None, 'FOObar'])])"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "RefOrderedDict(foo=\"FOO\", bar=[None, \"{foo}bar\"])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "RefOrderedDict([('foo', 'FOO'), ('bar', {'42': 'FOObar'})])"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "RefOrderedDict(foo=\"FOO\", bar={'42': \"{foo}bar\"})"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example revisited"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "# This gives us what we wanted above, without specifying any leading f:\n",
    "config = RefOrderedDict(\n",
    "    foo = \"FOO\",\n",
    "    bar = \"{foo}bar\" # should evaluate to \"FOObar\"\n",
    ")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "RefOrderedDict([('foo', 'FOO'), ('bar', 'FOObar')])"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "config"
   ]
  }
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