pyplot example with QT Designer

Question

I have seen many examples of integrating matplotlib with python2.6 and QT4 Designer using mplwidget and they work fine. I now need to integrate a pyplot with QT4 Designer but cannot find any examples. All of my attempts to integrate a pyplot graphic have ended in a seg fault. Can someone please direct me to a working example using Designer and pyplot?

Follow up: Okay, so I tried your solution but I'm still having issues. Unfortunately the machine I use for this code is not hooked up to the internet, so below is a fat finger of the pertinent parts of the code I am using:

from PyQt4.QtCore import *
from PyQt4.QtGui import *

from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
import MatplotlibWidget     # This is the code snippet you gave in your answer

.
.
.
def drawMap(self) :

    fig = plt.figure()  

    map = Basemap(projection='cyl', llcrnrlat = -90.0, urcrnrlat = 90.0, llcrnrlon = -180.0, urcrnrlon = 180.0, resolution = 'c')
    map.drawcoastlines()
    map.drawcountries()
    plt.show()


def drawMap_Qt(self) :

    self.ui.PlotWidget.figure = plt.figure()  # This is the Qt widget promoted to MatplotlibWidget

    map = Basemap(projection='cyl', llcrnrlat = -90.0, urcrnrlat = 90.0, llcrnrlon = -180.0, urcrnrlon = 180.0, resolution = 'c')
    map.drawcoastlines()
    map.drawcountries()
    self.ui.PlotWidget.show()

The function drawMap() works fine. It creates a separate window and plots the map. The drawMap_Qt() function results in a segmentation fault with no other errors. The end goal is to plot a contour on top of the map. I can do this with the drawMap() function. Of course, I can't even get to the contour part with the drawMap_Qt() function. Any insights as to why it is seg faulting would be greatly appreciated.

Answer 1

If you're referring to the mplwidget from Python(x,y) and WinPython, I think it does use pyplot, but I had trouble putting it in my python install so I just used this class:

from PyQt4 import QtGui
from matplotlib.figure import Figure
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt4agg import NavigationToolbar2QT as NavigationToolbar

class MatplotlibWidget(QtGui.QWidget):
    def __init__(self, parent=None, *args, **kwargs):
        super(MatplotlibWidget, self).__init__(parent)
        self.figure = Figure(*args, **kwargs)
        self.canvas = FigureCanvas(self.figure)
        self.toolbar = NavigationToolbar(self.canvas, self)
        layout = QtGui.QVBoxLayout()
        layout.addWidget(self.toolbar)
        layout.addWidget(self.canvas)
        self.setLayout(layout)

See also How to embed matplotib in pyqt - for Dummies.

Then in Qt Designer you need to create a promoted class, with base class: QWidget, promoted class name: MatplotlibWidget, and header file: the python script containing the MatplotlibWidget class (without the .py). You can add things like ax = self.figure.add_subplot(111), line = ax.plt(...) within the class or by calling methods of the figure attribute of an instance of the class.

Edit: So I was a bit wrong before, in general with embedded matplotlib widgets you need to use the object oriented methods and not the functions in pyplot. (This sort of explains what the difference is.) Using my snippet above as mymatplotlibwidget.py, try something like this. I don't have basemap installed, so this is somewhat of a guess, but from the examples you need to tell Basemap which axes to use.

import sys
from PyQt4 import QtGui
from mpl_toolkits.basemap import Basemap
from mymatplotlibwidget import MatplotlibWidget

app = QtGui.QApplication(sys.argv)
widget = MatplotlibWidget()
fig = widget.figure
ax = fig.add_subplot(111)
map = Basemap(..., ax=ax)
fig.canvas.draw()
widget.show()
app.exec_()