matplotlib and transparency figure

Question

I am working with the matplotlib library and PyQt5 with Python 3.6. I add a figure in a window I create, and I wish to set transparent

Answer 1

The problem occurs because the background image is set as a palette to the widget. This causes the canvas to inherit the palette and hence the canvas will also have the image as background, somehow overlaying the widget's background.

A solution would be to set the background of the canvas transparent. An easy way to do so are style sheets.

self.canvas.setStyleSheet("background-color:transparent;")

Note that this is not the same as setting the patches' facecolor to none. The figure has a background, which is controlled inside matplotlib, but the canvas, being a PyQt object also has a background.

Complete example:

import sys, os
from PyQt4.QtCore import Qt
from PyQt4.QtGui import *

import matplotlib
matplotlib.use('Qt4Agg') 
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt4agg import NavigationToolbar2QT as NavigationToolbar
from matplotlib.figure import Figure
import matplotlib.pyplot as plt
plt.rcParams['xtick.color'] ="w"
plt.rcParams['ytick.color'] ="w"
plt.rcParams['font.size'] = 14


class SecondWindow(QWidget):
    def __init__(self, parent=None):
        super(SecondWindow, self).__init__(parent)

        # CREATE FIGURE AND SETTINGS
        self.figure = plt.figure()
        self.figure.patch.set_facecolor("None")
        self.canvas = FigureCanvas(self.figure)
        self.axes = self.figure.add_subplot(111)
        self.axes.patch.set_alpha(0.5)

        ###### Make the background of the canvas transparent
        self.canvas.setStyleSheet("background-color:transparent;")

        self.p = QPalette()
        self.p.setBrush(QPalette.Background, QBrush(QPixmap("house.png")))
        self.setPalette(self.p)

        self.setLayout(QVBoxLayout())
        self.layout().addWidget(self.canvas,1)
        self.layout().setContentsMargins(50, 50, 50, 50)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    form = SecondWindow()
    form.show()
    sys.exit(app.exec_())

which might then look like