if pyside partially present ipython qtconsole fails to load even if pyqt4 present

[jamadagni]

On my Kubuntu Precise system I had installed python-pyside.qtcore and python-pyside.qtgui (but not pyside.qtsvg) for running another PySide-based program. Kubuntu of course has python-qt4 by default. In this setup, I found that running ipython qtconsole fails with the following error message:

$ ipython qtconsole
Traceback (most recent call last):
  File "/usr/bin/ipython", line 8, in <module>
    launch_new_instance()
  File "/usr/lib/python2.7/dist-packages/IPython/frontend/terminal/ipapp.py", line 402, in launch_new_instance
    app.initialize()
  File "<string>", line 2, in initialize
  File "/usr/lib/python2.7/dist-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/IPython/frontend/terminal/ipapp.py", line 302, in initialize
    super(TerminalIPythonApp, self).initialize(argv)
  File "<string>", line 2, in initialize
  File "/usr/lib/python2.7/dist-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/IPython/core/application.py", line 325, in initialize
    self.parse_command_line(argv)
  File "/usr/lib/python2.7/dist-packages/IPython/frontend/terminal/ipapp.py", line 297, in parse_command_line
    return super(TerminalIPythonApp, self).parse_command_line(argv)
  File "<string>", line 2, in parse_command_line
  File "/usr/lib/python2.7/dist-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/IPython/config/application.py", line 413, in parse_command_line
    return self.initialize_subcommand(subc, subargv)
  File "<string>", line 2, in initialize_subcommand
  File "/usr/lib/python2.7/dist-packages/IPython/config/application.py", line 84, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/IPython/config/application.py", line 349, in initialize_subcommand
    subapp = import_item(subapp)
  File "/usr/lib/python2.7/dist-packages/IPython/utils/importstring.py", line 40, in import_item
    module = __import__(package,fromlist=[obj])
  File "/usr/lib/python2.7/dist-packages/IPython/frontend/qt/console/qtconsoleapp.py", line 30, in <module>
    from IPython.external.qt import QtCore, QtGui
  File "/usr/lib/python2.7/dist-packages/IPython/external/qt.py", line 62, in <module>
    from PySide import QtCore, QtGui, QtSvg
ImportError: cannot import name QtSvg

What happens is as follows. In IPython/external/qt.py, line 24

QT_API = os.environ.get('QT_API')

gets set to a null string because there is no QT_API environment variable on my system, and the code then proceeds to line 27:

import PySide

which does not raise an ImportError because pyside.qtcore|qtgui are installed on my system, and hence line 31 is executed:

QT_API = QT_API_PYSIDE

which however later on leads to line 62:

from PySide import QtCore, QtGui, QtSvg

being executed which however does not work because the python-pyside.qtsvg package was not installed on my system.

I cannot fault the Debian packaging because as you can see on http://packages.debian.org/sid/ipython-qtconsole or http://packages.ubuntu.com/precise/ipython-qtconsole they do list a dependency on pyside.qtsvg but only if python-qt4 is not installed (which it is).

The solution would be to test for PySide having all the required modules before determining it as the appropriate Qt bindings. I propose the following patch for qt.py:

--- qt.py.orig  2012-04-22 10:40:27.000000000 +0530
+++ qt.py       2012-11-11 19:20:43.444954428 +0530
@@ -30,2 +30,3 @@
             raise ImportError
+        from PySide import QtCore, QtGui, QtSvg # checking that all required PySide modules are available 
         QT_API = QT_API_PYSIDE
@@ -35,3 +36,3 @@
             import PyQt4
-            from PyQt4 import QtCore
+            from PyQt4 import QtCore, QtGui, QtSvg # checking that all required PyQt4 modules are available
             if QtCore.PYQT_VERSION_STR < '4.7':
@@ -41,3 +42,3 @@
         except ImportError:
-            raise ImportError('Cannot import PySide >= 1.0.3 or PyQt4 >= 4.7')
+            raise ImportError('IPython requires QtCore, QtGui and QtSvg modules of either PySide >= 1.0.3 or PyQt4 >= 4.7')

but for some reason on my system modifying /usr/share/pyshared/IPython/external/qt.py thus gives the error:

$ ipython qtconsole
python: /build/buildd/sip4-4.13.2/siplib/siplib.c:7915: sip_api_can_convert_to_type: Assertion `(((td)->td_flags & 0x0007) == 0x0000) || (((td)->td_flags & 0x0007) == 0x0002)' failed.
[IPKernelApp] To connect another client to this kernel, use:
[IPKernelApp] --existing kernel-17799.json
Aborted (core dumped)

... so I leave it to the developers to fix this appropriately.

[takluyver]

I think this should already have been fixed, see 19502ae. The fix probably isn't in the version packaged in precise, though. If you want to use a newer version, you can add this PPA: https://launchpad.net/~jtaylor/+archive/ipython

I'll close this issue on the grounds that it's already fixed - if you can reproduce the problem with 0.13.1, we can reopen it

[juliantaylor]

see also gh-1431