When using pyqt, data transfer between subform and main form is needed.

The name of the new subform is DateDialog2.py

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


class DateDialog(QDialog):
    Signal_OneParameter = pyqtSignal(str)
    
    def __init__(self,parent =None):
        super(DateDialog,self).__init__(parent)
        self.setWindowTitle('Child window: used to transmit signals')
        
        #Add controls to layout
        layout = QVBoxLayout(self)
        
        self.label = QLabel(self)
        self.label.setText('The former transmits the built-in signal\n The latter sends a custom signal')
        
        self.datetime_inner = QDateTimeEdit(self)
        self.datetime_inner.setCalendarPopup(True)
        self.datetime_inner.setDateTime(QDateTime.currentDateTime())
        
        self.datetime_emit = QDateTimeEdit(self)
        self.datetime_emit.setCalendarPopup(True)
        self.datetime_emit.setDateTime(QDateTime.currentDateTime())
        
        layout.addWidget(self.label)
        layout.addWidget(self.datetime_inner)
        layout.addWidget(self.datetime_emit)
        
        #Use two buttons to connect the accept() and reject() slot functions respectively
        buttons = QDialogButtonBox(
            QDialogButtonBox.Ok | QDialogButtonBox.Cancel,
            Qt.Horizontal,self)
        buttons.accepted.connect(self.accept)
        buttons.rejected.connect(self.reject)
        
        self.datetime_emit.dateTimeChanged.connect(self.emit_signal)
        layout.addWidget(buttons)
        
    def emit_signal(self):
        date_str = self.datetime_emit.dateTime().toString()
        self.Signal_OneParameter.emit(date_str)

The name of the main form is CallDialogMainWin2.py

from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
import sys
from DateDialog2 import DateDialog
                   
class WinForm(QWidget):
    def __init__(self, parent =None):
        super(WinForm,self).__init__(parent)
        self.resize(400,90)
        self.setWindowTitle('Example of signal and slot transfer parameters')
        
        self.open_btn =  QPushButton('Acquisition time')
        self.lineEdit_inner = QLineEdit(self)
        self.lineEdit_emit = QLineEdit(self)
        self.open_btn.clicked.connect(self.openDialog)
        
        self.lineEdit_inner.setText('Time to receive the built-in signal of the subwindow')
        self.lineEdit_emit.setText('Time to accept custom signals from child windows')
        
        grid = QGridLayout()
        grid.addWidget(self.lineEdit_inner)
        grid.addWidget(self.lineEdit_emit)
        
        grid.addWidget(self.open_btn)
        self.setLayout(grid)
        
    def openDialog(self):
        dialog = DateDialog(self)
        '''Connect the built-in signal of the sub window with the slot function of the main window'''
        dialog.datetime_inner.dateTimeChanged.connect(self.deal_inner_slot)
        '''Connect custom signal of child window with slot function of main window'''
        dialog.Signal_OneParameter.connect(self.deal_emit_slot)
        dialog.show()
        
    def deal_inner_slot(self,date):
        self.lineEdit_inner.setText(date.toString())
        
    def deal_emit_slot(self,dateStr):
        self.lineEdit_emit.setText(dateStr)
        
if __name__=='__main__':
    app = QApplication(sys.argv)
    form = WinForm()
    form.show()
    sys.exit(app.exec_())
        

Operation effect

When you change the date on a subform, it is automatically passed to the main form

self.datetime_emit.dateTimeChanged.connect(self.emit_signal)

def emit_signal(self):
        date_str = self.datetime_emit.dateTime().toString()
        self.Signal_OneParameter.emit(date_str)

The key is how to realize the transmission of customized signals that meet specific conditions?

When the time of control datetime  exit changes, the slot function exit  Signal of the sub window will be triggered. In this slot function, the user-defined Signal signal -- OneParameter will be sent. This Signal function is used to pass the date  STR parameter to the slot function of the main function.

def openDialog(self):
        dialog = DateDialog(self)
        '''Connect the built-in signal of the sub window with the slot function of the main window'''
        dialog.datetime_inner.dateTimeChanged.connect(self.deal_inner_slot)
        '''Connect custom signal of child window with slot function of main window'''
        dialog.Signal_OneParameter.connect(self.deal_emit_slot)
        dialog.show()

The key of the main window is to bind the built-in signal and custom signal of the sub window to the slot function of the main window.

###Reference pyqt5 rapid development and Practice