PyQt Widget connect() and disconnect()

Question

Depending on a conditions I would like to connect/re-connect a button to a different function.

Let’s say I have a button:

myButton = QtGui.QPushButton()

For this example let’s say I check if there is an internet connection.

if connected == True:
    myButton.clicked.connect(function_A)

elif connected == False:
    myButton.clicked.connect(function_B)

First of all I would like to disconnect a button from any function it was already connected before the button is being re-assigned/re-connected to another function (function_A or function_B).
Secondly, I have already noticed that after the button is re-connected it takes an extra click for the button to pick up a new function. After the button is re-connected to another function it still attempts to run a previous function – a function to which a button was connected earlier (before a re-connection). Please advice. Thanks in advance!

EDITED LATER:

It appears a widget’s .disconnect() method can be used to disconnect a button from a function it it is connected.

myButton.disconnect()

Unfortunately .disconnect() throws an error if a widget is not connected to any function.
To get around it I am using Try/Except. But I would rather use a more elegant solution…

try: myButton.clicked.disconnect() 
except Exception: pass

Asked By: alphanumeric

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Source

Answer 1

Try this:

from PyQt4 import QtGui as gui

app = gui.QApplication([])

myButton = gui.QPushButton()

def function_A():
    myButton.clicked.disconnect() #this disconnect all!
    myButton.clicked.connect(function_B)
    print 'function_A'

def function_B():
    myButton.clicked.disconnect(function_B) #this disconnect function_B
    myButton.clicked.connect(function_A)
    print 'function_B'

myButton.clicked.connect(function_A)
myButton.setText("Click me!")
myButton.show()

app.exec_()

Answered By: Alvaro Fuentes

Answer 2

If you need to reconnect signals in many places, then you could define a generic utility function like this:

def reconnect(signal, newhandler=None, oldhandler=None):        
    try:
        if oldhandler is not None:
            while True:
                signal.disconnect(oldhandler)
        else:
            signal.disconnect()
    except TypeError:
        pass
    if newhandler is not None:
        signal.connect(newhandler)

...

if connected:
    reconnect(myButton.clicked, function_A)
else:
    reconnect(myButton.clicked, function_B)

(NB: the loop is needed for safely disconnecting a specific handler, because it may have been connected multple times, and disconnect(slot) only removes one connection at a time.).

Answered By: ekhumoro

Answer 3

Concise way for 3.4+ with contextlib.suppress:

with contextlib.suppress(RuntimeError):
    button.clicked.disconnect()
button.connect(func_a if condition else func_b)

Answered By: johnson

PyQt Widget connect() and disconnect()

Question:

EDITED LATER:

Answers: