How to resize font size in PyQt5 GUI?

Question

I have shortly finished my WhatsApp bot. However I found a problem over the days, trying to use it on my normal laptop than my monitor. The screensize changes and with it the PyQt5 GUI. The big problem is that I set the font size and that it doesn't change by resizing other than the buttons usw.

Here is my Code:

from functools import cached_property
import sys
import threading
import time

from selenium.webdriver.common.keys import Keys
from selenium import webdriver
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions
from selenium.webdriver.common.by import By

from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *


class Worker:
    def start(self, amount, adressed, message):
        threading.Thread(target=self._execute, args=(amount, adressed, message), daemon=True).start()

    def _execute(self, amount, adressed, message):
        profile_path = "user-data-dir=/home/daniel/.config/google-chrome/storing1"

        options = webdriver.ChromeOptions()
        options.add_argument(profile_path)
        browser = webdriver.Chrome(executable_path="./chromedriver", options=options)
        browser.get("https://web.whatsapp.com")

        time.sleep(5)
        search = WebDriverWait(browser, 500).until(expected_conditions.presence_of_element_located(
            (By.CSS_SELECTOR, "#side > div.SgIJV > div > label > div > div._2_1wd.copyable-text.selectable-text")))
        search.send_keys(adressed)
        time.sleep(1)
        search.send_keys(Keys.ENTER)
        send = WebDriverWait(browser, 500).until(expected_conditions.presence_of_element_located((By.CSS_SELECTOR,
                                                                                                  "#main > footer > div.vR1LG._3wXwX.copyable-area > div._2A8P4._2A1WX > div > div._2_1wd.copyable-text.selectable-text")))

        for i in range(amount):
            send.send_keys(message)
            send.send_keys(Keys.ENTER)



class interface(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initMe()

    def initMe(self):
        self.boldFont = QFont()
        self.boldFont.setBold(True)
        self.setGeometry(1200, 250, 600, 500)
        self.title = self.setWindowTitle("Whatsapp Bot interface")
        self.Layout_components()
        self.labels()
        self.input()
        self.button()
        self.setFont(QFont("Arial", 15))
        self.setWindowIcon(QIcon("Bot.png"))

        self.show()

    def Layout_components(self):
        self.exit_ = QAction(QIcon("Bot.png"), "Exit", self)
        self.stop_ = QAction(QIcon("Bot.png"), "Stop", self)
        self.start_ = QAction(QIcon("Bot.png"), "Start", self)
        self.exit_.triggered.connect(self.exit)
        self.stop_.triggered.connect(self.stop)
        self.start_.triggered.connect(self.start)

        menubar = self.menuBar()
        file = menubar.addMenu("Bot")
        file.addAction(self.exit_)
        file.addAction(self.stop_)
        file.addAction(self.start_)

    def labels(self):
        labelp1 = QLabel("picture", self)
        labelp1.setPixmap(QPixmap("Bot.png"))
        labelp1.setGeometry(340, 100, 210, 180)

        labelp2 = QLabel("picture1", self)
        labelp2.setPixmap(QPixmap("whatsapp_symbol.png"))
        labelp2.setScaledContents(True)
        labelp2.resize(80, 80)
        labelp2.setGeometry(50, 400, 80, 80)

        label1 = QLabel("description", self)
        label1.setGeometry(50, 40, 500, 50)
        label1.setText(
            "Welcome to my Whatsappbot. Are you ready to annoy other people with endless spam up. Have fun!!!")
        label1.setFont(QFont("Arial", 14))
        label1.setStyleSheet("border : 2px solid black;")
        label1.setWordWrap(True)

        label2 = QLabel("adress", self)
        label2.setGeometry(50, 100, 150, 50)
        label2.setText("adressed to: ")

        label2 = QLabel("message", self)
        label2.setGeometry(50, 300, 150, 50)
        label2.setText("message: ")

        label2 = QLabel("amount", self)
        label2.setGeometry(50, 200, 200, 50)
        label2.setText("amount of messages: ")

        self.label_input = QLabel("counter", self)
        self.label_input.setGeometry(170, 260, 80, 20)
        self.label_input.setFont(QFont("Arial", 15))
        self.label_input.setAlignment(Qt.AlignCenter)
        self.label_input.setStyleSheet("border:2px solid black")

    def input(self):
        self.input_adressed = QLineEdit(self)
        self.input_adressed.setGeometry(50, 150, 150, 30)

        self.input_message = QLineEdit(self)
        self.input_message.setGeometry(50, 350, 150, 30)

        self.input_amount = QSlider(self)
        self.input_amount.setGeometry(50, 240, 100, 70)
        self.input_amount.setMaximum(1000)

        self.input_amount.valueChanged.connect(self.label_input.setNum)

    def button(self):
        self.but_stop = QPushButton("Stop", self)
        self.but_stop.setGeometry(340, 360, 210, 50)
        self.but_stop.setFont(self.boldFont)
        self.but_stop.clicked.connect(self.stop)

        self.but_start = QPushButton("Start", self)
        self.but_start.setGeometry(340, 300, 210, 50)
        self.but_start.setFont(self.boldFont)
        self.but_start.clicked.connect(self.start)

        self.but_exit = QPushButton("Exit", self)
        self.but_exit.setGeometry(340, 420, 210, 50)
        self.but_exit.setFont(self.boldFont)
        self.but_exit.clicked.connect(self.exit)

    @cached_property
    def worker(self):
        return Worker()

    @property
    def amount(self):
        value = self.input_amount.value()
        return value

    @property
    def adressed(self):
        return self.input_adressed.text()

    @property
    def message(self):
        return self.input_message.text()

    def stop(self):
        print("programm stopps ...")
        QCoreApplication.quit()


    def exit(self):
        QCoreApplication.quit()

    def start(self):
        pop_up = QMessageBox(self)
        pop_up.setWindowTitle("Start Bot")
        pop_up.setText("Do you really wanna start the spam ?!")
        pop_up.setIcon(QMessageBox.Question)
        pop_up.setStandardButtons(QMessageBox.Cancel | QMessageBox.No | QMessageBox.Yes)
        pop_up.setDefaultButton(QMessageBox.Yes)
        if pop_up.exec_() == QMessageBox.Yes:
            print("programm starts ...")
            self.worker.start(self.amount, self.adressed, self.message)


app = QApplication(sys.argv)
x = interface()
sys.exit(app.exec_())

Answer 1

1. use setFont(): it sets the default font for the target; you can get the current default font using something.font(), then use font.setPointSize() (or setPointSizeF() for float values, if the font allows it) and then call setFont(font) on the target.
2. use font[-*] in the target setStyleSheet();