access instance variable by name from function - python-3.x

Question

I need to make a UI for a class which makes a number of calculations from a set of variables. The code roughly looks like this:
class MainWindow:
def __init__(self):
pulse = Pulse()
self.var1_lineEdit.textEdited.connect(self.set_attribute(pulse, "var1", new_value))
self.var2_lineEdit.textEdited.connect(self.set_attribute(pulse, "var2", new_value))
self.var3_lineEdit.textEdited.connect(self.set_attribute(pulse, "var3", new_value))
....
def set_attribute(pulse, var_name, value):
# get value from line edit
# update value in pulse
# update other calculations
class Pulse:
def __init__(self):
var1 = 1
var2 = 2
var3 = 3
....
My problem here is how to code set_attribute. Is there a way to access individual variables of another class by passing the name as a function argument? I would like to avoid having to define a new function for each variable.
Or is there a simpler way to do this? I am not very familiar with OOP and the proper way of coding UIs.

Answer 1

EDIT
The signal/slot connections you've proposed will get you in trouble. Signals are connected to slots using the connect function, which accepts a python callable as its argument--not the function call itself. That's the difference between
widget.textChanged.connect(self.set_attribute) # right syntax
widget.textChanged.connect(self.set_attribute()) # wrong syntax
So then, how do you tell set_attribute what to do? ekhumoro informed me the error of my ways re: use of QSignalMapper. It's an outdated technique. Best to simply use lambda functions (or partials) to get the desired effect.
I updated my demo for use of lambdas
For the purposes of this demo, I've created a simple QMainWindow with two QLineEdit widgets and a QPushButton.
# file ui_main.py
from PyQt5 import QtCore, QtGui, QtWidgets
class Ui_MainWindow(object):
def setupUi(self, MainWindow):
MainWindow.setObjectName("MainWindow")
MainWindow.resize(359, 249)
self.centralwidget = QtWidgets.QWidget(MainWindow)
self.centralwidget.setObjectName("centralwidget")
self.formLayoutWidget = QtWidgets.QWidget(self.centralwidget)
self.formLayoutWidget.setGeometry(QtCore.QRect(0, 0, 351, 51))
self.formLayoutWidget.setObjectName("formLayoutWidget")
self.formLayout = QtWidgets.QFormLayout(self.formLayoutWidget)
self.formLayout.setObjectName("formLayout")
self.configParam1Label = QtWidgets.QLabel(self.formLayoutWidget)
self.configParam1Label.setObjectName("configParam1Label")
self.formLayout.setWidget(0, QtWidgets.QFormLayout.LabelRole, self.configParam1Label)
self.configEntry = QtWidgets.QLineEdit(self.formLayoutWidget)
self.configEntry.setObjectName("configEntry")
self.formLayout.setWidget(0, QtWidgets.QFormLayout.FieldRole, self.configEntry)
self.configParam2Label = QtWidgets.QLabel(self.formLayoutWidget)
self.configParam2Label.setObjectName("configParam2Label")
self.formLayout.setWidget(1, QtWidgets.QFormLayout.LabelRole, self.configParam2Label)
self.configEntry2 = QtWidgets.QLineEdit(self.formLayoutWidget)
self.configEntry2.setObjectName("configEntry2")
self.formLayout.setWidget(1, QtWidgets.QFormLayout.FieldRole, self.configEntry2)
self.pulseButton = QtWidgets.QPushButton(self.centralwidget)
self.pulseButton.setGeometry(QtCore.QRect(130, 140, 75, 23))
self.pulseButton.setObjectName("pulseButton")
MainWindow.setCentralWidget(self.centralwidget)
self.retranslateUi(MainWindow)
QtCore.QMetaObject.connectSlotsByName(MainWindow)
def retranslateUi(self, MainWindow):
_translate = QtCore.QCoreApplication.translate
MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
self.configParam1Label.setText(_translate("MainWindow", "Config Param 1"))
self.configParam2Label.setText(_translate("MainWindow", "Config Param 2"))
self.pulseButton.setText(_translate("MainWindow", "GetPulse"))
In another file, after some imports, define Pulse--a simple class that contains two attributes
# file main.py
from PyQt5.QtCore import (QSignalMapper, pyqtSlot)
from PyQt5.QtWidgets import (QApplication, QMainWindow, QMessageBox)
from ui_main import Ui_MainWindow
class Pulse:
def __init__(self):
self.param_one = None
self.param_two = None
Now, define MainWindow, setting up its UI and giving it a Pulse:
class MainWindow(QMainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.pulse = Pulse()
self.ui = Ui_MainWindow()
self.ui.setupUi(self)
self.widget_one = self.ui.configEntry
self.widget_two = self.ui.configEntry2
self.pulse_button = self.ui.pulseButton
self.widget_one.textChanged.connect(lambda: self.widget_handler('param_one', self.widget_one.text()))
self.widget_one.textChanged.connect(lambda: self.widget_handler('param_two', self.widget_two.text()))
def widget_handler(self, attr, value):
setattr(self.pulse,attr,value)
def handler(self, idx):
widget, attr = self.attribute_widget_list[idx]
widget_value = widget.text()
setattr(self.pulse,attr,widget_value)
setattr is equivalent to, for example, self.pulse.param_one = widget_value.
To prove it works, let's use that QPushButton to probe the state of Pulse:
#pyqtSlot()
def on_pulseButton_clicked(self):
message = QMessageBox()
message.setText("{} - {}".format(self.pulse.param_one, self.pulse.param_two))
message.exec()
Here I'm using a different signal/slot connection scheme, which you can read about here
And here's how we run the script:
if __name__ == '__main__':
import sys
app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec_())
Hope that helps!