The PythonQwt project was initiated to solve -at least temporarily- the obsolescence issue of PyQwt (the Python-Qwt C++ bindings library) which is no longer maintained. The idea was to translate the original Qwt C++ code to Python and then to optimize some parts of the code by writing new modules based on NumPy and other libraries.

The PythonQwt package consists of a single Python package named qwt and of a few other files (examples, doc, ...).

See documentation online or PDF for more details on the library and changelog for recent history of changes.

import qwt
import numpy as np

app = qwt.qt.QtGui.QApplication([])

# Create plot widget
plot = qwt.QwtPlot("Trigonometric functions")
plot.insertLegend(qwt.QwtLegend(), qwt.QwtPlot.BottomLegend)

# Create two curves and attach them to plot
x = np.linspace(-10, 10, 500)
qwt.QwtPlotCurve.make(x, np.cos(x), "Cosinus", plot, linecolor="red", antialiased=True)
qwt.QwtPlotCurve.make(x, np.sin(x), "Sinus", plot, linecolor="blue", antialiased=True)

# Resize and show plot
plot.resize(600, 300)
plot.show()

app.exec_()

The GUI-based test launcher may be executed from Python:

from qwt import tests
tests.run()

or from the command line (script name depends on Python major version number):

PythonQwt-py3

Tests may also be executed in unattended mode:

PythonQwt-tests-py3 --mode unattended

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 more powerful features already exist in guiqwt: QwtPlotZoomer, QwtCounter, QwtEventPattern, QwtPicker, QwtPlotPicker.

Only the following plot items are currently implemented in qwt (the only plot items needed by guiqwt): QwtPlotItem (base class), QwtPlotItem, QwtPlotMarker, QwtPlotSeriesItem and QwtPlotCurve.

See "Overview" section in documentation for more details on API limitations when comparing to Qwt.

• Python >=2.6 or Python >=3.2
• PyQt4 >=4.4 or PyQt5 >= 5.5 (or PySide2, still experimental, see below)
• QtPy >= 1.3
• NumPy >= 1.5

Try running the curvebenchmark1.py test with PyQt5 and PySide: you will notice a huge performance issue with PySide2 (see screenshot above). This is due to the fact that QPainter.drawPolyline is much more efficient in PyQt5 than it is in PySide2 (see this bug report).

As a consequence, until this bug is fixed in PySide2, we still recommend using PyQt5 instead of PySide2 when it comes to representing huge data sets.

However, PySide2 support was significatively improved betwen PythonQwt V0.8.0 and V0.8.1 thanks to the new array2d_to_qpolygonf function (see the part related to PySide2 in the code below).

def array2d_to_qpolygonf(xdata, ydata):
    """
    Utility function to convert two 1D-NumPy arrays representing curve data
    (X-axis, Y-axis data) into a single polyline (QtGui.PolygonF object).
    This feature is compatible with PyQt4, PyQt5 and PySide2 (requires QtPy).

    License/copyright: MIT License © Pierre Raybaut 2020.

    :param numpy.ndarray xdata: 1D-NumPy array (numpy.float64)
    :param numpy.ndarray ydata: 1D-NumPy array (numpy.float64)
    :return: Polyline
    :rtype: QtGui.QPolygonF
    """
    dtype = np.float
    if not (
        xdata.size == ydata.size == xdata.shape[0] == ydata.shape[0]
        and xdata.dtype == ydata.dtype == dtype
    ):
        raise ValueError("Arguments must be 1D, float64 NumPy arrays with same size")
    size = xdata.size
    polyline = QPolygonF(size)
    if PYSIDE2:  # PySide2 (obviously...)
        address = shiboken2.getCppPointer(polyline.data())[0]
        buffer = (ctypes.c_double * 2 * size).from_address(address)
    else:  # PyQt4, PyQt5
        buffer = polyline.data()
        buffer.setsize(2 * size * np.finfo(dtype).dtype.itemsize)
    memory = np.frombuffer(buffer, dtype)
    memory[: (size - 1) * 2 + 1 : 2] = xdata
    memory[1 : (size - 1) * 2 + 2 : 2] = ydata
    return polyline

From the source package:

python setup.py install

• Copyright © 2002 Uwe Rathmann, for the original Qwt C++ code
• Copyright © 2015 Pierre Raybaut, for the Qwt C++ to Python translation and optimization
• Copyright © 2015 Pierre Raybaut, for the PythonQwt specific and exclusive Python material

• Copyright © 2009-2013 Pierre Raybaut
• Copyright © 2013-2015 The Spyder Development Team

• Copyright © 2003-2009 Gerard Vermeulen, for the original PyQwt code
• Copyright © 2015 Pierre Raybaut, for the PyQt5/PySide port and further developments (e.g. ported to PythonQwt API)

The qwt Python package was partly (>95%) translated from Qwt C++ library: the associated code is distributed under the terms of the LGPL license. The rest of the code was either wrote from scratch or strongly inspired from MIT licensed third-party software.

See included LICENSE file for more details about licensing terms.