How to create dependent combo box with QComboBox widgets | PyQt5 Tutorial

In this tutorial, we will learn how to create dependent combo box with PyQt5 in Python.

A combo box (some people called it drop-down) is a graphical control allowing a user to pick an item from a list. Often time, there will be scenario where you want to specify a combo box list depending on a parent value. So in this tutorial, I will walk you through the steps to create a dependent combo box using PyQt5.

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Source Code:

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QComboBox, QHBoxLayout
from PyQt5.QtGui import QStandardItemModel, QStandardItem, QFont

class AppDemo(QWidget):
    def __init__(self):
        super().__init__()
        self.setFixedSize(700, 100)

        mainLayout = QHBoxLayout()

        self.model = QStandardItemModel()

        # states
        self.comboStates = QComboBox()
        self.comboStates.setFixedSize(325, 50)
        self.comboStates.setFont(QFont('', 12))
        self.comboStates.setModel(self.model)

        # cities
        self.comboCities = QComboBox()
        self.comboCities.setFixedSize(325, 50)
        self.comboCities.setFont(QFont('', 12))
        self.comboCities.setModel(self.model)

        # add data
        for k, v in data.items():
            state = QStandardItem(k)
            self.model.appendRow(state)
            for value in v:
                city = QStandardItem(value)
                state.appendRow(city)

        self.comboStates.currentIndexChanged.connect(self.updateStateCombo)
        self.updateStateCombo(0)

        mainLayout.addWidget(self.comboStates)
        mainLayout.addWidget(self.comboCities)
        self.setLayout(mainLayout)

    def updateStateCombo(self, index):
        indx = self.model.index(index, 0, self.comboStates.rootModelIndex())
        self.comboCities.setRootModelIndex(indx)
        self.comboCities.setCurrentIndex(0)


data = {
    'California': ['San Francisco', 'Oakland', 'Los Angeles'],
    'Illinois': ['Chicago', 'Springfield', 'Evanston'],
    'Texas': ['Austin', 'Houston', 'San Antonio']
}

app = QApplication(sys.argv)        
demo = AppDemo()
demo.show()
sys.exit(app.exec_())