.. _qtconsole:

=========================
A Qt Console for IPython
=========================

We now have a version of IPython, using the new two-process :ref:`ZeroMQ Kernel
<ipythonzmq>`, running in a PyQt_ GUI.  This is a very lightweight widget that
largely feels like a terminal, but provides a number of enhancements only
possible in a GUI, such as inline figures, proper multiline editing with syntax
highlighting, graphical calltips, and much more.

.. figure:: ../_static/qtconsole.png
    :width: 400px
    :alt: IPython Qt console with embedded plots
    :align: center
    :target: ../_static/qtconsole.png

    The Qt console for IPython, using inline matplotlib plots.

To get acquainted with the Qt console, type `%guiref` to see a quick
introduction of its main features.

The Qt frontend has hand-coded emacs-style bindings for text navigation. This
is not yet configurable.

.. tip::

   Since the Qt console tries hard to behave like a terminal, by default it
   immediately executes single lines of input that are complete.  If you want
   to force multiline input, hit :key:`Ctrl-Enter` at the end of the first line
   instead of :key:`Enter`, and it will open a new line for input.  At any
   point in a multiline block, you can force its execution (without having to
   go to the bottom) with :key:`Shift-Enter`.

``%loadpy``
===========

The new ``%loadpy`` magic takes any python script (must end in '.py'), and
pastes its contents as your next input, so you can edit it before
executing. The script may be on your machine, but you can also specify a url,
and it will download the script from the web. This is particularly useful for
playing with examples from documentation, such as matplotlib.

.. sourcecode:: ipython

    In [6]: %loadpy http://matplotlib.sourceforge.net/plot_directive/mpl_examples/mplot3d/contour3d_demo.py

    In [7]: from mpl_toolkits.mplot3d import axes3d
       ...: import matplotlib.pyplot as plt
       ...: 
       ...: fig = plt.figure()
       ...: ax = fig.add_subplot(111, projection='3d')
       ...: X, Y, Z = axes3d.get_test_data(0.05)
       ...: cset = ax.contour(X, Y, Z)
       ...: ax.clabel(cset, fontsize=9, inline=1)
       ...: 
       ...: plt.show()

Pylab
=====

One of the most exciting features of the new console is embedded matplotlib
figures. You can use any standard matplotlib GUI backend (Except native MacOSX)
to draw the figures, and since there is now a two-process model, there is no
longer a conflict between user input and the drawing eventloop.

.. image:: figs/besselj.png
    :width: 519px

.. display:

:func:`display`
***************

An additional function, :func:`display`, will be added to the global namespace
if you specify the ``--pylab`` option at the command line. The IPython display
system provides a mechanism for specifying PNG or SVG (and more)
representations of objects for GUI frontends. By default, IPython registers
convenient PNG and SVG renderers for matplotlib figures, so you can embed them
in your document by calling :func:`display` on one or more of them. This is
especially useful for saving_ your work.

.. sourcecode:: ipython

    In [5]: plot(range(5)) # plots in the matplotlib window
    
    In [6]: display(gcf()) # embeds the current figure in the qtconsole
    
    In [7]: display(*getfigs()) # embeds all active figures in the qtconsole

If you have a reference to a matplotlib figure object, you can always display
that specific figure:

.. sourcecode:: ipython

   In [1]: f = figure()

   In [2]: plot(rand(100))
   Out[2]: [<matplotlib.lines.Line2D at 0x7fc6ac03dd90>]

   In [3]: display(f)

   # Plot is shown here

   In [4]: title('A title')
   Out[4]: <matplotlib.text.Text at 0x7fc6ac023450>

   In [5]: display(f)

   # Updated plot with title is shown here.

.. _inline:

``--pylab=inline``
******************

If you want to have all of your figures embedded in your session, instead of
calling :func:`display`, you can specify ``--pylab=inline`` when you start the
console, and each time you make a plot, it will show up in your document, as if
you had called :func:`display(fig)`.


.. _saving:

Saving and Printing
===================

IPythonQt has the ability to save your current session, as either HTML or
XHTML. If you have been using :func:`display` or inline_ pylab, your figures
will be PNG in HTML, or inlined as SVG in XHTML. PNG images have the option to
be either in an external folder, as in many browsers' "Webpage, Complete"
option, or inlined as well, for a larger, but more portable file.

The widget also exposes the ability to print directly, via the default print
shortcut or context menu.


.. Note:: 

    Saving is only available to richtext Qt widgets, which are used by default,
    but if you pass the ``--plain`` flag, saving will not be available to you.


See these examples of :download:`png/html<figs/jn.html>` and
:download:`svg/xhtml <figs/jn.xhtml>` output. Note that syntax highlighting
does not survive export. This is a known issue, and is being investigated.

Colors and Highlighting
=======================

Terminal IPython has always had some coloring, but never syntax
highlighting. There are a few simple color choices, specified by the ``colors``
flag or ``%colors`` magic:

* LightBG for light backgrounds
* Linux for dark backgrounds
* NoColor for a simple colorless terminal

The Qt widget has full support for the ``colors`` flag used in the terminal shell.

The Qt widget, however, has full syntax highlighting as you type, handled by
the `pygments`_ library. The ``style`` argument exposes access to any style by
name that can be found by pygments, and there are several already
installed. The ``colors`` argument, if unspecified, will be guessed based on
the chosen style. Similarly, there are default styles associated with each
``colors`` option.


Screenshot of ``ipython qtconsole --colors=linux``, which uses the 'monokai'
theme by default:

.. image:: figs/colors_dark.png
    :width: 627px
    
.. Note::

    Calling ``ipython qtconsole -h`` will show all the style names that
    pygments can find on your system.

You can also pass the filename of a custom CSS stylesheet, if you want to do
your own coloring, via the ``stylesheet`` argument.  The default LightBG
stylesheet:

.. sourcecode:: css

    QPlainTextEdit, QTextEdit { background-color: white;
            color: black ;
            selection-background-color: #ccc}
    .error { color: red; }
    .in-prompt { color: navy; }
    .in-prompt-number { font-weight: bold; }
    .out-prompt { color: darkred; }
    .out-prompt-number { font-weight: bold; }

Fonts
=====

The QtConsole has configurable via the ConsoleWidget. To change these, set the
``font_family`` or ``font_size`` traits of the ConsoleWidget. For instance, to
use 9pt Anonymous Pro::

    $> ipython qtconsole --ConsoleWidget.font_family="Anonymous Pro" --ConsoleWidget.font_size=9

Process Management
==================

With the two-process ZMQ model, the frontend does not block input during
execution. This means that actions can be taken by the frontend while the
Kernel is executing, or even after it crashes. The most basic such command is
via 'Ctrl-.', which restarts the kernel.  This can be done in the middle of a
blocking execution. The frontend can also know, via a heartbeat mechanism, that
the kernel has died. This means that the frontend can safely restart the
kernel.

Multiple Consoles
*****************

Since the Kernel listens on the network, multiple frontends can connect to it.
These do not have to all be qt frontends - any IPython frontend can connect and
run code.  When you start ipython qtconsole, there will be an output line,
like::

    [IPKernelApp] To connect another client to this kernel, use:
    [IPKernelApp] --existing --shell=60690 --iopub=44045 --stdin=38323 --hb=41797

Other frontends can connect to your kernel, and share in the execution. This is
great for collaboration. The `-e` flag is for 'external'. Starting other
consoles with that flag will not try to start their own, but rather connect to
yours. Ultimately, you will not have to specify each port individually, but for
now this copy-paste method is best.

By default (for security reasons), the kernel only listens on localhost, so you
can only connect multiple frontends to the kernel from your local machine. You
can specify to listen on an external interface by specifying the ``ip``
argument::

    $> ipython qtconsole --ip=192.168.1.123

If you specify the ip as 0.0.0.0, that refers to all interfaces, so any
computer that can see yours can connect to the kernel.

.. warning::

    Since the ZMQ code currently has no security, listening on an
    external-facing IP is dangerous.  You are giving any computer that can see
    you on the network the ability to issue arbitrary shell commands as you on
    your machine. Be very careful with this.


Stopping Kernels and Consoles
*****************************

Since there can be many consoles per kernel, the shutdown mechanism and dialog
are probably more complicated than you are used to. Since you don't always want
to shutdown a kernel when you close a window, you are given the option to just
close the console window or also close the Kernel and *all other windows*. Note
that this only refers to all other *local* windows, as remote Consoles are not
allowed to shutdown the kernel, and shutdowns do not close Remote consoles (to
allow for saving, etc.).

Rules:

    * Restarting the kernel automatically clears all *local* Consoles, and prompts remote
      Consoles about the reset.
    * Shutdown closes all *local* Consoles, and notifies remotes that
      the Kernel has been shutdown.
    * Remote Consoles may not restart or shutdown the kernel.

Qt and the QtConsole
====================

An important part of working with the QtConsole when you are writing your own
Qt code is to remember that user code (in the kernel) is *not* in the same
process as the frontend.  This means that there is not necessarily any Qt code
running in the kernel, and under most normal circumstances there isn't. If,
however, you specify ``--pylab=qt`` at the command-line, then there *will* be a
:class:`QCoreApplication` instance running in the kernel process along with
user-code. To get a reference to this application, do:

.. sourcecode:: python

    from PyQt4 import QtCore
    app = QtCore.QCoreApplication.instance()
    # app will be None if there is no such instance

A common problem listed in the PyQt4 Gotchas_ is the fact that Python's garbage
collection will destroy Qt objects (Windows, etc.) once there is no longer a
Python reference to them, so you have to hold on to them.  For instance, in:

.. sourcecode:: python

    def make_window():
        win = QtGui.QMainWindow()
    
    def make_and_return_window():
        win = QtGui.QMainWindow()
        return win

:func:`make_window` will never draw a window, because garbage collection will
destroy it before it is drawn, whereas :func:`make_and_return_window` lets the
caller decide when the window object should be destroyed.  If, as a developer,
you know that you always want your objects to last as long as the process, you
can attach them to the QApplication instance itself:

.. sourcecode:: python
    
    # do this just once:
    app = QtCore.QCoreApplication.instance()
    app.references = set()
    # then when you create Windows, add them to the set
    def make_window():
        win = QtGui.QMainWindow()
        app.references.add(win)

Now the QApplication itself holds a reference to ``win``, so it will never be
garbage collected until the application itself is destroyed.

.. _Gotchas: http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/gotchas.html#garbage-collection

Regressions
===========

There are some features, where the qt console lags behind the Terminal
frontend:

* !cmd input: Due to our use of pexpect, we cannot pass input to subprocesses
   launched using the '!' escape, so you should never call a command that
   requires interactive input.  For such cases, use the terminal IPython.  This
   will not be fixed, as abandoning pexpect would significantly degrade the
   console experience.

* Use of ``\b`` and ``\r`` characters in the console: these are control
  characters that allow the cursor to move backwards on a line, and are used to
  display things like in-place progress bars in a terminal.  We currently do
  not support this, but it is being tracked as issue 629_.

.. _629:  https://github.com/ipython/ipython/issues/629

.. [PyQt] PyQt4 http://www.riverbankcomputing.co.uk/software/pyqt/download
.. [pygments] Pygments http://pygments.org/
