.. only:: html


.. index:: Plugins; Debugging

**********************************************
IDE settings for writing and debugging plugins
**********************************************

.. warning:: |outofdate|

.. contents::
   :local:


Although each programmer has his preferred IDE/Text editor, here are some
recommendations for setting up popular IDE's for writing and debugging QGIS
Python plugins.

A note on configuring your IDE on Windows
=========================================

On Linux there is no additional configuration needed to develop plugins.
But on Windows you need to make sure you that you have the same environment
settings and use the same libraries and interpreter as QGIS. The fastest
way to do this, is to modify the startup batch file of QGIS.

If you used the OSGeo4W Installer, you can find this under the ``bin`` folder
of your OSGeo4W install. Look for something like
:file:`C:\\OSGeo4W\\bin\\qgis-unstable.bat`.

For using `Pyscripter IDE <https://github.com/pyscripter/pyscripter>`_, here's what
you have to do:

* Make a copy of :file:`qgis-unstable.bat` and rename it ``pyscripter.bat``.
* Open it in an editor. And remove the last line, the one that starts QGIS.
* Add a line that points to your Pyscripter executable and add the
  command line argument that sets the version of Python to be used
* Also add the argument that points to the folder where Pyscripter can
  find the Python dll used by QGIS, you can find this under the bin folder
  of your OSGeoW install

  .. code-block:: bat

    @echo off
    SET OSGEO4W_ROOT=C:\OSGeo4W
    call "%OSGEO4W_ROOT%"\bin\o4w_env.bat
    call "%OSGEO4W_ROOT%"\bin\gdal16.bat
    @echo off
    path %PATH%;%GISBASE%\bin
    Start C:\pyscripter\pyscripter.exe --python25 --pythondllpath=C:\OSGeo4W\bin

Now when you double click this batch file it will start Pyscripter, with the
correct path.

More popular than Pyscripter, Eclipse is a common choice among developers. In
the following sections, we will be explaining how to configure it for
developing and testing plugins. To prepare your environment for using Eclipse
in Windows, you should also create a batch file and use it to start Eclipse.

To create that batch file, follow these steps:

* Locate the folder where :file:`qgis_core.dll` resides in. Normally this is
  :file:`C:\\OSGeo4W\\apps\\qgis\\bin`, but if you compiled your own QGIS
  application this is in your build folder in :file:`output/bin/RelWithDebInfo`
* Locate your :file:`eclipse.exe` executable.
* Create the following script and use this to start eclipse when developing
  QGIS plugins.

.. code-block:: bat

  call "C:\OSGeo4W\bin\o4w_env.bat"
  set PATH=%PATH%;C:\path\to\your\qgis_core.dll\parent\folder
  C:\path\to\your\eclipse.exe

Debugging using Eclipse and PyDev
=================================

Installation
------------

To use Eclipse, make sure you have installed the following

* `Eclipse <https://eclipse.org>`_
* `Aptana Studio 3 Plugin <www.aptana.com/>`_ or `PyDev <https://www.pydev.org>`_
* QGIS 2.x

Preparing QGIS
--------------

There is some preparation to be done on QGIS itself. Two plugins are of
interest: **Remote Debug** and **Plugin reloader**.

* Go to :menuselection:`Plugins --> Manage and Install plugins...`
* Search for *Remote Debug* ( at the moment it's still experimental, so enable
  experimental plugins under the :guilabel:`Options` tab in case it does not show up).
  Install it.
* Search for *Plugin reloader* and install it as well. This will let you reload
  a plugin instead of having to close and restart QGIS to have the plugin
  reloaded.

Setting up Eclipse
------------------

In Eclipse, create a new project. You can select *General Project* and link
your real sources later on, so it does not really matter where you place this
project.

.. figure:: img/eclipsenewproject.png
   :align: center

   Eclipse project

Now right-click your new project and choose :menuselection:`New --> Folder`.

Click :guilabel:`Advanced` and choose :guilabel:`Link to alternate location
(Linked Folder)`. In case you already have sources you want to debug, choose
these. In case you don't, create a folder as it was already explained.

Now in the view :guilabel:`Project Explorer`, your source tree pops up and you
can start working with the code. You already have syntax highlighting and all
the other powerful IDE tools available.

Configuring the debugger
------------------------

To get the debugger working, switch to the Debug perspective in Eclipse
(:menuselection:`Window --> Open Perspective --> Other --> Debug`).

Now start the PyDev debug server by choosing :menuselection:`PyDev --> Start
Debug Server`.

Eclipse is now waiting for a connection from QGIS to its debug server and when
QGIS connects to the debug server it will allow it to control the python
scripts. That's exactly what we installed the *Remote Debug* plugin for. So
start QGIS in case you did not already and click the bug symbol.

Now you can set a breakpoint and as soon as the code hits it, execution will
stop and you can inspect the current state of your plugin. (The breakpoint is
the green dot in the image below, set one by double clicking in the white space
left to the line you want the breakpoint to be set).

.. figure:: img/breakpoint.png
   :align: center

   Breakpoint

A very interesting thing you can make use of now is the debug console. Make
sure that the execution is currently stopped at a break point, before you
proceed.

Open the Console view (:menuselection:`Window --> Show view`). It will show the
:guilabel:`Debug Server` console which is not very interesting. But there is a
button :guilabel:`Open Console` which lets you change to a more interesting PyDev
Debug Console. Click the arrow next to the :guilabel:`Open Console` button and choose
*PyDev Console*. A window opens up to ask you which console you want to start.
Choose *PyDev Debug Console*. In case its greyed out and tells you to Start the
debugger and select the valid frame, make sure that you've got the remote
debugger attached and are currently on a breakpoint.

.. figure:: img/console-buttons.png
   :align: center

   PyDev Debug Console

You have now an interactive console which let's you test any commands from
within the current context. You can manipulate variables or make API calls or
whatever you like.

A little bit annoying is, that every time you enter a command, the console
switches back to the Debug Server. To stop this behavior, you can click the
*Pin Console* button when on the Debug Server page and it should remember this
decision at least for the current debug session.

Making eclipse understand the API
---------------------------------

A very handy feature is to have Eclipse actually know about the QGIS API. This
enables it to check your code for typos. But not only this, it also enables
Eclipse to help you with autocompletion from the imports to API calls.

To do this, Eclipse parses the QGIS library files and gets all the information
out there. The only thing you have to do is to tell Eclipse where to find the
libraries.

Click :menuselection:`Window --> Preferences --> PyDev --> Interpreter --> Python`.

You will see your configured python interpreter in the upper part of the window
(at the moment python2.7 for QGIS) and some tabs in the lower part. The
interesting tabs for us are *Libraries* and *Forced Builtins*.

.. figure:: img/interpreter-libraries.png
   :align: center

   PyDev Debug Console

First open the Libraries tab. Add a New Folder and choose the python folder of
your QGIS installation. If you do not know where this folder is (it's not the
plugins folder) open QGIS, start a python console and simply enter ``qgis`` and
press Enter. It will show you which QGIS module it uses and its path. Strip the
trailing ``/qgis/__init__.pyc`` from this path and you've got the path you are
looking for.

You should also add your plugins folder here (it is in :file:`python/plugins`
under the :ref:`user profile <user_profiles>` folder).

Next jump to the *Forced Builtins* tab, click on *New...* and enter ``qgis``.
This will make Eclipse parse the QGIS API. You probably also want Eclipse to
know about the PyQt4 API. Therefore also add PyQt4 as forced builtin. That
should probably already be present in your libraries tab.

Click *OK* and you're done.

.. note::
   Every time the QGIS API changes (e.g. if you're compiling QGIS master and
   the SIP file changed), you should go back to this page and simply click
   *Apply*. This will let Eclipse parse all the libraries again.


Debugging using PDB
===================

If you do not use an IDE such as Eclipse, you can debug using PDB, following
these steps.

First add this code in the spot where you would like to debug

::

 # Use pdb for debugging
 import pdb
 # These lines allow you to set a breakpoint in the app
 pyqtRemoveInputHook()
 pdb.set_trace()

Then run QGIS from the command line.

On Linux do:

.. code-block:: bash

 $ ./Qgis

On macOS do:

.. code-block:: bash

 $ /Applications/Qgis.app/Contents/MacOS/Qgis

And when the application hits your breakpoint you can type in the console!

.. index:: plugins; testing

**TODO:**
    Add testing information


.. Substitutions definitions - AVOID EDITING PAST THIS LINE
   This will be automatically updated by the find_set_subst.py script.
   If you need to create a new substitution manually,
   please add it also to the substitutions.txt file in the
   source folder.

.. |outofdate| replace:: `Despite our constant efforts, information beyond this line may not be updated for QGIS 3. Refer to https://qgis.org/pyqgis/master for the python API documentation or, give a hand to update the chapters you know about. Thanks.`