PyQt5 front-end and python back-end

QtFranchise · wrote on 27 Aug 2022, 16:07

Hi I just created a simple Serial Terminal App. Its UI is designed using Qt Designer and imported in the project using UIC module. Just wanted to know that the way I used PyQt5 with Python is he correct one any comments and input are welcome. Since Qt uses signals and slots for communication used QThread subclass that will generate necessary signal which is captured by the Event Loop and since I did not find a way to send back response (like button press, text change etc) used class instance and passed that to the respective member for further processing.

It is working well for now. But, I need someone to look into the code and provide inputs on the same.

main.py

from PyQt5 import QtWidgets
from gui import UI
import sys


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    window = UI()
    window.show()
    sys.exit(app.exec_())

serial_control.py

from PyQt5.QtCore import QThread
from PyQt5 import QtCore
import serial
import serial.tools.list_ports
import time


class SerialControl(QThread):
    status = QtCore.pyqtSignal(bool)
    received = QtCore.pyqtSignal(str)

    def __init__(self):
        super().__init__()
        self.VID = 0x2341
        self.PID = 0x3d
        self.serial = None
        self.input = ""
        self.output = ""
        self.connected = False

    def find_port(self):
        for port in serial.tools.list_ports.comports():
            if (port.vid == self.VID) and (port.pid == self.PID):
                print("Port: ", port.device)
                return port.device
        return None

    def run(self):
        while True:
            if not self.connected:
                port = self.find_port()
                if port:
                    try:
                        self.serial = serial.Serial(port, 115200, timeout=0.25)
                        if self.serial:
                            self.connected = True
                            print("Connected")
                            self.status.emit(True)
                    except serial.SerialException:
                        pass
            elif self.connected:
                try:
                    if not self.serial.is_open:
                        self.serial.open()
                except AttributeError:
                    pass

                try:
                    if self.serial.in_waiting:
                        self.input = self.serial.readline().decode("utf-8")
                        print("Received: ", self.input)
                        self.received.emit(self.input)
                    elif self.output:
                        time.sleep(0.25)
                        self.serial.write(self.output.encode())
                        print("Sent: ", self.output)
                        self.output = ""
                except OSError:
                    print("Disconnected")
                    self.connected = False
                    self.status.emit(False)

            time.sleep(0.25)

gui.py

from PyQt5 import QtWidgets, uic
from serial_control import SerialControl


class UI(QtWidgets.QMainWindow):
    def __init__(self):
        super(UI, self).__init__()
        self.terminal = SerialControl()
        self.setup_ui()

    def setup_ui(self):
        uic.loadUi('ui.ui', self)
        self.btn_send.clicked.connect(self.send)
        self.start_terminal()

    def start_terminal(self):
        self.terminal.status.connect(self.control_button)
        self.terminal.received.connect(self.receive)
        self.terminal.start()

    def control_button(self, state):
        self.btn_send.setEnabled(state)

    def send(self):
        self.terminal.output = self.lineEdit.text()
        self.lineEdit.setText('')

    def receive(self, msg):
        self.textEdit.setText(msg)

ui.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>715</width>
    <height>510</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Serial Terminal</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <layout class="QVBoxLayout" name="verticalLayout_3">
    <item>
     <layout class="QVBoxLayout" name="verticalLayout" stretch="1,0,5">
      <item>
       <widget class="QWidget" name="horizontalWidget" native="true">
        <property name="sizePolicy">
         <sizepolicy hsizetype="Preferred" vsizetype="Fixed">
          <horstretch>0</horstretch>
          <verstretch>0</verstretch>
         </sizepolicy>
        </property>
        <layout class="QHBoxLayout" name="horizontalLayout" stretch="1,0,0">
         <property name="spacing">
          <number>6</number>
         </property>
         <property name="leftMargin">
          <number>5</number>
         </property>
         <property name="topMargin">
          <number>5</number>
         </property>
         <property name="rightMargin">
          <number>5</number>
         </property>
         <property name="bottomMargin">
          <number>5</number>
         </property>
         <item>
          <widget class="QLineEdit" name="lineEdit"/>
         </item>
         <item>
          <spacer name="horizontalSpacer">
           <property name="orientation">
            <enum>Qt::Horizontal</enum>
           </property>
           <property name="sizeHint" stdset="0">
            <size>
             <width>40</width>
             <height>20</height>
            </size>
           </property>
          </spacer>
         </item>
         <item>
          <widget class="QPushButton" name="btn_send">
           <property name="enabled">
            <bool>false</bool>
           </property>
           <property name="text">
            <string>Send</string>
           </property>
          </widget>
         </item>
        </layout>
       </widget>
      </item>
      <item>
       <spacer name="verticalSpacer">
        <property name="orientation">
         <enum>Qt::Vertical</enum>
        </property>
        <property name="sizeType">
         <enum>QSizePolicy::Fixed</enum>
        </property>
        <property name="sizeHint" stdset="0">
         <size>
          <width>20</width>
          <height>10</height>
         </size>
        </property>
       </spacer>
      </item>
      <item>
       <widget class="QGroupBox" name="groupBox">
        <property name="title">
         <string>Received</string>
        </property>
        <layout class="QVBoxLayout" name="verticalLayout_2">
         <property name="spacing">
          <number>0</number>
         </property>
         <property name="leftMargin">
          <number>0</number>
         </property>
         <property name="topMargin">
          <number>0</number>
         </property>
         <property name="rightMargin">
          <number>0</number>
         </property>
         <property name="bottomMargin">
          <number>0</number>
         </property>
         <item>
          <widget class="QTextEdit" name="textEdit"/>
         </item>
        </layout>
       </widget>
      </item>
     </layout>
    </item>
   </layout>
  </widget>
  <widget class="QStatusBar" name="statusbar"/>
 </widget>
 <resources/>
 <connections/>
</ui>

SGaist · 29 Aug 2022, 06:49

Hi,

Before analyzing your code deeper, why not use Qt's QSerialPort class that is asynchronous rather than adding threading to the mix ?

QtFranchise · S SGaist 27 Aug 2022, 17:30

@SGaist Yes that may be a choice. But I preferred pyserial because it did my work easy. Will consider QSerialPort when working next time. Any other inputs please.

SGaist · wrote on 29 Aug 2022, 19:38

You should:

provide a clean way to quit your thread
use a cleaner setup/tear down for the opening and closing of your device
why all these sleep call ?