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PyQtGraph – Getting Opacity Property of Error Bar Graph

  • Last Updated : 21 Nov, 2021

In this article, we will see how we can get the opacity property of the error bar graph in the PyQtGraph module. The PyQtGraph is a graphics and user interface library for Python that provides functionality commonly required in designing and science applications. Its primary goals are to provide fast, interactive graphics for displaying data (plots, video, etc.). Error bars are graphical representations of the variability of data and used on graphs to indicate the error or uncertainty in a reported measurement. They give a general idea of how precise a measurement is, or conversely, how far from the reported value the true value might be. Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc. It can be set with the help of the setOpacity() method.

We can create a plot window and create error bar graph on it with the help of commands given below: 

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# creating a pyqtgraph plot window
plt = pg.plot()

# creating a error bar item object
error = pg.ErrorBarItem(x=x, y=y, top=top, bottom=bottom, beam=0.5)

In order to do this, we use opacity() method with the error bar item object:



Syntax : error.opacity()
Argument : It takes no argument
Return : It returns float value 

Below is the implementation: 

Python3




# importing Qt widgets
from PyQt5.QtWidgets import *
 
# importing system
import sys
 
# importing numpy as np
import numpy as np
 
# importing pyqtgraph as pg
import pyqtgraph as pg
from PyQt5.QtGui import *
from PyQt5.QtCore import *
 
from collections import namedtuple
 
 
class Window(QMainWindow):
 
    def __init__(self):
        super().__init__()
 
        # setting title
        self.setWindowTitle("PyQtGraph")
 
        # setting geometry
        self.setGeometry(100, 100, 600, 500)
 
        # icon
        icon = QIcon("skin.png")
 
        # setting icon to the window
        self.setWindowIcon(icon)
 
        # calling method
        self.UiComponents()
 
        # showing all the widgets
        self.show()
 
    # method for components
    def UiComponents(self):
 
        # creating a widget object
        widget = QWidget()
 
        # creating a label
        label = QLabel("Geeksforgeeks Error Bar plot")
 
        # setting minimum width
        label.setMinimumWidth(130)
 
        # making label do word wrap
        label.setWordWrap(True)
 
        # setting configuration options
        pg.setConfigOptions(antialias=True)
 
        # creating x-axis values
        x = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
 
        # creating y-axis values
        y = np.array([5, 4, 3, 2, 5, 6, 4, 8, 9, 8])
 
        # creating upper bound values
        top = np.array([2, 2, 2, 2, 2, 2, 2, 2, 2, 2])
 
        # creating lower bound values
        bottom = np.array([2, 2, 2, 2, 2, 2, 2, 2, 2, 2])
 
        # creating a plot window
        plt = pg.plot()
 
        # creating a error bar item
        error = pg.ErrorBarItem(beam=0.5)
 
        # setting data to error bar item
        error.setData(x=x, y=y, top=top, bottom=bottom)
 
        # adding error bar item to the plot window
        plt.addItem(error)
 
        # plotting the data on plot window
        plt.plot(x, y, symbol='o', pen={'color': 0.8, 'width': 2})
 
        # Creating a grid layout
        layout = QGridLayout()
 
        # minimum width value of the label
        label.setMinimumWidth(130)
 
        # setting this layout to the widget
        widget.setLayout(layout)
 
        # adding label in the layout
        layout.addWidget(label, 1, 0)
 
        # plot window goes on right side, spanning 3 rows
        layout.addWidget(plt, 0, 1, 3, 1)
 
        # setting this widget as central widget of the main window
        self.setCentralWidget(widget)
 
        # setting opacity of error bar item
        error.setOpacity(0.3)
 
        # getting opacity  of the error bar item
        value = error.opacity()
 
        # setting text to the label
        label.setText("Opacity : " + str(value))
 
 
# create pyqt5 app
App = QApplication(sys.argv)
 
# create the instance of our Window
window = Window()
 
# start the app
sys.exit(App.exec())

Output:




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