How Can I Pass Extra Arguments to Qt Slots in PyQt?

Passing Extra Arguments through Qt Slots

In PyQt applications, slots are member functions that are invoked when a signal is emitted. These signals can be emitted by various Qt objects, such as buttons or widgets. By default, slots receive the parameters passed by the signal. However, it is also possible to pass additional arguments to slots.

Problem: Passing Variable Through Slots

Consider the following scenario: You have a function that defines a variable named DiffP. You want to pass this variable to a slot that is connected to a button click event.

class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        [...]
        self.button.clicked.connect(self.some_slot)

    def some_slot(self):
        # Here you want to access the 'DiffP' variable defined in another function

Solution: Using Lambda Functions

One way to pass extra arguments through slots is to use lambda functions. Lambda functions are anonymous functions that can be defined inline. You can create a lambda function that takes both the default slot parameters and the extra arguments you want to pass.

class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        [...]
        self.button.clicked.connect(lambda: self.some_slot("DiffP"))

    def some_slot(self, DiffP):
        # Here you can access the 'DiffP' variable

In this example, the lambda function takes the extra argument DiffP and passes it to the some_slot function.

Solution: Using functools.partial

Another way to pass extra arguments through slots is to use the functools.partial function. The partial function creates a new function that is partially applied with some arguments. You can use partial to create a function that takes only the default slot parameters and pass the extra arguments as bound arguments.

from functools import partial

class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        [...]
        self.button.clicked.connect(partial(self.some_slot, "DiffP"))

    def some_slot(self, DiffP):
        # Here you can access the 'DiffP' variable

In this example, the partial function creates a new function that takes only the button_or_id parameter and binds the DiffP argument to it. When the slot is invoked, the new function will be called with the correct arguments.

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