(magic-command)=
# Magic commands 
**(5 minutes)**

:::{note}
In Jupyter, "magic" refers to additional commands added by Jupyter to
the kernel environment that aren't normally part of that kernel's
language.[^f54] I'm going to start with a slightly exotic magic command
because I think you'll find it useful.
:::

In a new cell in the Python notebook we just worked with, execute this
command:[^f55]

    %jsroot on

:::{note}
As a general rule, magic commands begin with the percent sign "%".[^f56]
:::

Draw the canvas again:

    my_canvas.Draw()

Move the cursor over the new plot.

:::{note}
Ah, that's more like it! The plot is not interactive in the same way as
in X-Windows ROOT, but you can get a lot done. Play around a bit,
looking at tooltips and right-clicking. Note the faint icons below the
lower left-hand corner of the plot.

If you execute `%lsmagic` you'll see a list of available magic
commands. There's probably more here than you can absorb right now.[^f57]
Here are examples of the magic commands I find to be the most useful:

    %mkdir subdirectory
    %cp ~seligman/root-class/jsroot-test.ipynb subdirectory
    %ls subdirectory
    %less c1.C
    %man root
    %cd subdirectory

The above commands are "line magics," which are executed line-by-line
within a cell. There are also "cell magics" that affect the contents of
the entire cell in which they appear; they must appear as the first line
in a cell. They begin with a double "%". Examples:

-   `%%writefile` <filename> (write the cell to file <filename>);

-   `%%timeit` (execute the cell many times and determine the average
    execution time);

-   `%%sh` (execute the cell as a UNIX shell script).
:::

[^f54]: No, nothing to do with Doctor Strange or Gandalf, though you may
    find yourself muttering "You shall not pass!" as you work with ROOT.

[^f55]: Note that the `%jsroot` magic command is only available in
    Python-based notebooks after you've executed `import ROOT` or
    `from ROOT import...` In ROOT C++ notebooks it's built-in.

    "JSROOT" is short for "Javascript ROOT"; it's an [evolving project](https://github.com/root-project/jsroot/blob/master/docs/JSROOT.md) to
    bring more interactivity of ROOT graphics into web browsers.

[^f56]: Well... not really. There's an option `(%automagic on|off`)
    that allows you to omit the leading %. In this tutorial I'll always
    include the % prefix to make it clear when a command is "magic".

[^f57]: Here are more details about [magic commands](https://ipython.readthedocs.io/en/stable/interactive/magics.html).