.. _qtconsole:

=========================
IPython as a QtGUI widget
=========================

We now have a version of IPython, using the new two-process :ref:`ZeroMQ Kernel <ipythonzmq>`,
running in a PyQt_ GUI.

Overview
========

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

.. seealso:: 

    :ref:`The original IPython-Qt project description. <ipython_qt>`
    
``%loadpy``
===========

The ``%loadpy`` magic has been added, just for the GUI frontend. It 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

.. pastefig:

:func:`pastefig`
****************

An additional function, :func:`pastefig`, will be added to the global namespace if you
specify the ``pylab`` argument. This takes the active figures in matplotlib, and embeds
them in your document. This is especially useful for saving_ your work.

.. _inline:

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

If you want to have all of your figures embedded in your session, instead of calling
:func:`pastefig`, you can specify ``pylab=inline``, and each time you make a plot, it
will show up in your document, as if you had called :func:`pastefig`.


.. _saving:

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

IPythonQt has the ability to save your current session, as either HTML or XHTML. If you
have been using :func:`pastefig` 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::

    To connect another client to this kernel, use:
    --external shell=62109 iopub=62110 stdin=62111 hb=62112

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. We hope
to have these fixed by 0.11 release.

    * !cmd input: Due to our use of pexpect, we cannot pass input to subprocesses launched
      using the '!' escape. (this will not be fixed).

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