PyQtGraph - Setting Pen of Line in Line Graph

Last Updated : 15 Jan, 2022

In this article we will see how we can set pen of the line in line graph of the PyQtGraph module. 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.) A line chart or line plot or line graph or curve chart is a type of chart which displays information as a series of data points called 'markers' connected by straight line segments. It is a basic type of chart common in many fields. Line graph is created with the help of plot class in PyQtGraph. Pen is basically painter object used to draw the line on the window, with the help of pen we can set the color of the line.

We can create a plot window and create lines on it with the help of commands given below

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

# plotting line in green color
# with dot symbol as x, not a mandatory field
line = plt.plot(x, y, pen='g', symbol='x', symbolPen='g', symbolBrush=0.2, name='green')

In order to do this we use setPen method with the line object
Syntax : line.setPen(QColor(168, 34, 3))
Argument : It takes QColor/QBrush/QPen object as argument
Return : It returns None

Below is the implementation

Python3

# importing Qt widgets
from PyQt5.QtWidgets import * import sys

# importing pyqtgraph as pg
import pyqtgraph as pg
from PyQt5.QtGui import *

# Bar Graph class
class BarGraphItem(pg.BarGraphItem):

    # constructor which inherit original
    # BarGraphItem
    def __init__(self, *args, **kwargs):
        pg.BarGraphItem.__init__(self, *args, **kwargs)

    # creating a mouse double click event
    def mouseDoubleClickEvent(self, e):

        # setting scale
        self.setScale(0.2)



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 new label
        label = QLabel("GeeksforGeeks Line Plot")

        # making it multiline
        label.setWordWrap(True)

        # y values to plot by line 1
        y = [2, 8, 6, 8, 6, 11, 14, 13, 18, 19]

        # y values to plot by line 2
        y2 = [3, 1, 5, 8, 9, 11, 16, 17, 14, 16]
        x = range(0, 10)

        # create plot window object
        plt = pg.plot()

        # showing x and y grids
        plt.showGrid(x = True, y = True)

        # adding legend
        plt.addLegend()

        # set properties of the label for y axis
        plt.setLabel('left', 'Vertical Values', units ='y')

        # set properties of the label for x axis
        plt.setLabel('bottom', 'Horizontal Values', units ='s')

        # setting horizontal range
        plt.setXRange(0, 10)

        # setting vertical range
        plt.setYRange(0, 20)

        # plotting line in green color
        # with dot symbol as x, not a mandatory field
        line1 = plt.plot(x, y, pen ='g', symbol ='x', symbolPen ='g', symbolBrush = 0.2, name ='green')

        # plotting line2 with blue color
        # with dot symbol as o
        line2 = plt.plot(x, y2, pen ='b', symbol ='o', symbolPen ='b', symbolBrush = 0.2, name ='blue')

        # setting pen of the line 1
        line1.setPen(QColor(168, 34, 3))





        # label minimum width
        label.setMinimumWidth(150)

        # Creating a grid layout
        layout = QGridLayout()

        # setting this layout to the widget
        widget.setLayout(layout)

        # adding label to 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)





# create pyqt5 app
App = QApplication(sys.argv)

# create the instance of our Window
window = Window()

# start the app
sys.exit(App.exec())