{
  "cells": [
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "# Accessing Python Syntax Trees"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "It is also possible to access code that is written in Python. This works using the `ast` module, and works as follows:"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 1,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Module(body=[FunctionDef(name='f', args=arguments(args=[arg(arg='x', annotation=None), arg(arg='y', annotation=None)], vararg=None, kwonlyargs=[], kw_defaults=[], kwarg=None, defaults=[]), body=[Return(value=BinOp(left=BinOp(left=BinOp(left=Num(n=2), op=Mult(), right=Name(id='x', ctx=Load())), op=Add(), right=BinOp(left=Name(id='y', ctx=Load()), op=Pow(), right=Num(n=2))), op=Add(), right=Num(n=5)))], decorator_list=[], returns=None)])\n"
          ]
        }
      ],
      "source": [
        "SRC = \"\"\"\n",
        "def f(x, y):\n",
        "    return 2*x + y**2 + 5\n",
        "\"\"\"\n",
        "\n",
        "import ast\n",
        "tree = ast.parse(SRC)\n",
        "\n",
        "print(ast.dump(tree))"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "It is possible to transcribe the expressions here into the form discussed earlier."
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 2,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "2*x + y**2 + 5\n"
          ]
        }
      ],
      "source": [
        "from pymbolic.interop.ast import ASTToPymbolic\n",
        "expr = ASTToPymbolic()(tree.body[0].body[0].value)\n",
        "print(expr)"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "But beware when defining languages this way. Python has very well-defined semantics, and the user will expect that your way of executing their code is a good match for their mental model of what the code should do. As such, it may be better to start with a \"blank slate\" in terms of language design, so as to not run afoul of already formed expectations."
      ]
    }
  ],
  "metadata": {
    "kernelspec": {
      "display_name": "Python 3",
      "language": "python",
      "name": "python3"
    },
    "language_info": {
      "codemirror_mode": {
        "name": "ipython",
        "version": 3
      },
      "file_extension": ".py",
      "mimetype": "text/x-python",
      "name": "python",
      "nbconvert_exporter": "python",
      "pygments_lexer": "ipython3",
      "version": "3.5.0+"
    }
  },
  "nbformat": 4,
  "nbformat_minor": 0
}