Pure Python implementation of Qwt - Python 3

 The qwt package is a pure Python implementation of Qwt C++ library
 with the following limitations.
 .
 The following `Qwt` classes won't be reimplemented in `qwt` because most
 powerful features already exist in `guiqwt`:
   * QwtPlotZoomer
   * QwtCounter
   * QwtEventPattern
   * QwtPicker
   * QwtPlotPicker
 .
 QwtClipper is not implemented yet (and it will probably be very
 difficult or impossible to implement it in pure Python without
 performance issues). As a consequence, when zooming in a plot curve,
 the entire curve is still painted (in other words, when working with
 large amount of data, there is no performance gain when zooming in).
 .
 This is the Python 3 version of the package.