Replace use of 2to3 with six

[rahulporuri]

modernize was used to make the necessary changes.
The changes introduced in this PR are :

• remove use of xrange
• remove use of basestring and unicode
• update use of exception statement
• update use of raise statement
• remove/replace use of print statement
• make imports explcitly local
• update modules imports to be 2/3 compat e.g. cStringIO, thread and cPickle
• update dict-related methods i.e. has_key, values, keys, items
• update function object attrs e.g. func_name

[codecov-io]

Codecov Report

Merging #355 into master will increase coverage by 0.04%.
The diff coverage is 45.17%.

@@            Coverage Diff             @@
##           master     #355      +/-   ##
==========================================
+ Coverage   35.12%   35.17%   +0.04%     
==========================================
  Files         463      463              
  Lines       25732    25769      +37     
  Branches     3831     3830       -1     
==========================================
+ Hits         9039     9063      +24     
- Misses      16311    16324      +13     
  Partials      382      382

Impacted Files	Coverage Δ
pyface/ui/wx/layered_panel.py	28.78% <0%> (ø)	⬆️
pyface/ui/wx/image_list.py	0% <0%> (ø)	⬆️
pyface/ui/qt4/tasks/editor_area_pane.py	22.22% <0%> (ø)	⬆️
pyface/wx/spreadsheet/default_renderer.py	0% <0%> (ø)	⬆️
pyface/ui/qt4/wizard/wizard.py	0% <0%> (ø)	⬆️
pyface/tree/trait_dict_node_type.py	0% <0%> (ø)	⬆️
pyface/wx/grid/grid_model.py	0% <0%> (ø)	⬆️
pyface/dock/dock_window.py	21.85% <0%> (ø)	⬆️
pyface/ui/wx/ipython_widget.py	0% <0%> (ø)	⬆️
pyface/wx/spreadsheet/virtual_model.py	0% <0%> (ø)	⬆️
... and 65 more

---

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[rahulporuri]

That was surprising. There was a broken import which got fixed in the commit ac76443 which has surprisingly fixed the test failures. Not sure why though.

As can be seen from the travis job - https://travis-ci.org/enthought/pyface/builds/494249473, the test failures are only on python 2.

The test failures on Python seem to be related to qt-api preparation. See traceback below for python 2 and toolkit pyqt on rh6.

$ edm run -e pyface-test-2.7-pyqt -- python -m nose pyface/tasks/tests/test_dock_pane_toggle_group.py 
E
======================================================================
ERROR: Failure: ValueError (API 'QDate' has already been set to version 1. Pyface expects PyQt API 2 under Python 2. Either import Pyface before any other Qt-using packages, or explicitly set the API before importing any other Qt-using packages.)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/rporuri/.edm/envs/pyface-test-2.7-pyqt/lib/python2.7/site-packages/nose/loader.py", line 420, in loadTestsFromName
    addr.filename, addr.module)
  File "/home/rporuri/.edm/envs/pyface-test-2.7-pyqt/lib/python2.7/site-packages/nose/importer.py", line 47, in importFromPath
    return self.importFromDir(dir_path, fqname)
  File "/home/rporuri/.edm/envs/pyface-test-2.7-pyqt/lib/python2.7/site-packages/nose/importer.py", line 94, in importFromDir
    mod = load_module(part_fqname, fh, filename, desc)
  File "/home/rporuri/Github/work/pyface/pyface/tasks/tests/test_dock_pane_toggle_group.py", line 5, in <module>
    from pyface.tasks.action.api import SMenu, SMenuBar, SGroup, \
  File "/home/rporuri/Github/work/pyface/pyface/tasks/action/api.py", line 13, in <module>
    from .dock_pane_toggle_group import DockPaneToggleGroup
  File "/home/rporuri/Github/work/pyface/pyface/tasks/action/dock_pane_toggle_group.py", line 5, in <module>
    from pyface.action.api import Action, ActionItem, Group
  File "/home/rporuri/Github/work/pyface/pyface/action/api.py", line 15, in <module>
    from .action_item import ActionItem
  File "/home/rporuri/Github/work/pyface/pyface/action/action_item.py", line 25, in <module>
    from pyface.toolkit import toolkit_object
  File "/home/rporuri/Github/work/pyface/pyface/toolkit.py", line 27, in <module>
    toolkit = toolkit_object = find_toolkit('pyface.toolkits')
  File "/home/rporuri/Github/work/pyface/pyface/base_toolkit.py", line 272, in find_toolkit
    toolkit = plugin.load()
  File "/home/rporuri/.edm/envs/pyface-test-2.7-pyqt/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2408, in load
    return self.resolve()
  File "/home/rporuri/.edm/envs/pyface-test-2.7-pyqt/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2414, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/home/rporuri/Github/work/pyface/pyface/ui/qt4/init.py", line 18, in <module>
    from pyface.qt import QtCore, QtGui, qt_api
  File "/home/rporuri/Github/work/pyface/pyface/qt/__init__.py", line 82, in <module>
    prepare_pyqt4()
  File "/home/rporuri/Github/work/pyface/pyface/qt/__init__.py", line 44, in prepare_pyqt4
    raise ValueError(msg)
ValueError: API 'QDate' has already been set to version 1. Pyface expects PyQt API 2 under Python 2. Either import Pyface before any other Qt-using packages, or explicitly set the API before importing any other Qt-using packages.

----------------------------------------------------------------------

[corranwebster]

Thanks for doing this - it has been on my to-do list for a while but have not gotten around to it.

[corranwebster]

A couple of glitches in print statements, but otherwise looks good to me.