{
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   "cell_type": "markdown",
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   "source": [
    "# Running Python code"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Interactively (demo)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "To run Python code interactively, one can use the standard Python prompt, which can be launched by typing ``python`` in your standard shell:\n",
    "\n",
    "    $ python\n",
    "    Python 3.4.1 (default, May 21 2014, 21:17:51) \n",
    "    [GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin\n",
    "    Type \"help\", \"copyright\", \"credits\" or \"license\" for more information.\n",
    "    >>>\n",
    "\n",
    "The ``>>>`` indicates that Python is ready to accept commands. If you type ``a = 1`` then press enter, this will assign the value ``1`` to ``a``. If you then type ``a`` you will see the value of ``a`` (this is equivalent to ``print a``):\n",
    "\n",
    "    >>> a = 1\n",
    "    >>> a\n",
    "    1\n",
    "\n",
    "The Python shell can execute any Python code, even multi-line statements, though it is often more convenient to use Python non-interactively for such cases.\n",
    "\n",
    "The default Python shell is limited, so we will use the IPython (or interactive Python) shell here. This is an add-on package that adds many features to the default Python shell, including the ability to edit and navigate the history of previous commands, as well as the ability to tab-complete variable and function names. To start up IPython, type:\n",
    "\n",
    "    $ ipython\n",
    "    Python 3.4.1 (default, May 21 2014, 21:17:51) \n",
    "    Type \"copyright\", \"credits\" or \"license\" for more information.\n",
    "\n",
    "    IPython 2.1.0 -- An enhanced Interactive Python.\n",
    "    ?         -> Introduction and overview of IPython's features.\n",
    "    %quickref -> Quick reference.\n",
    "    help      -> Python's own help system.\n",
    "    object?   -> Details about 'object', use 'object??' for extra details.\n",
    "\n",
    "    In [1]:\n",
    "\n",
    "The first time you start up IPython, it will display a message which you can skip over by pressing ``ENTER``. The ``>>>`` symbols are now replaced by ``In [x]``, and output, when present, is prepended with ``Out [x]``. If we now type the same commands as before, we get:\n",
    "\n",
    "    In [1]: a = 1\n",
    "\n",
    "    In [2]: a\n",
    "    Out[2]: 1\n",
    "\n",
    "If you now type the up arrow twice, you will get back to ``a = 1``.\n",
    "\n",
    "To exit the Python shell at any time and return to the command prompt of the terminal, type ``exit()``."
   ]
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