Pass extra arguments to PyQt slot without losing default signal arguments

Question

A PyQt button event can be connected in the normal way to a function so that the function receives the default signal arguments (in this case the button checked state):

def connections(self):
    my_button.clicked.connect(self.on_button)

def on_button(self, checked):
    print checked   # prints "True"

Or, the default signal arguments can be overridden using lambda:

def connections(self):
    my_button.clicked.connect(lambda: self.on_button('hi'))

def on_button(self, message):
    print message   # prints "hi"

Is there a nice way to keep both signal arguments so it can be directly received by a function like below?

def on_button(self, checked, message):
    print checked, message   # prints "True, hi"

Answer 1

Your lambda could take an argument:

def connections(self):
    my_button.clicked.connect(lambda checked: self.on_button(checked, 'hi'))

def on_button(self, checked, message):
    print checked, message   # prints "True, hi"

Or you could use functools.partial:

# imports the functools module
import functools 

def connections(self):
    my_button.clicked.connect(functools.partial(self.on_button, 'hi'))

def on_button(self, message, checked):
    print checked, message   # prints "True, hi"