Passing Arguments with Newstyle signals in PyQT

Question

I've been having some trouble with a set of dynamically created buttons in PyQT.

I'm using a list to create buttons corresponding to different values. Because each button is different, I need to have them pass an argument to the "Button Clicked" function identifying themselves separately so I can perform different actions with them. Here is what I have so far:

for x in self.buttons:
    name = str(x)
    button = QtGui.QPushButton(Frame)
    button.setText(name)
    cp_result = self.changeProject(name)
    if cp_result is None:
        print 'changeProject(%s) is None!', name
    else:
        print 'changeProject(%s) is OK (%r)', name, cp_result
        #button.clicked.connect(cp_result)
    setattr(self, "btn_%s" % name, button)
    self.btnList.append(button)

def changeProject(self, name):
    for x in self.btnList:
        if x.isDown:
            #Change UI Frame to blahblah
    return 'A String'

Working with Alex, this is the latest code, testing a return value on changeProject, which clearly cannot be a string, but I still need to determine which button is pressed between the auto-generated buttons.

Current error: TypeError: connect() slot argument should be a callable or a signal, not 'str'

Answer 1

You can add attribute dynamically to objects using setattr

for x in buttons:
    name = str(x)
    button = QtGui.QPushButton(Frame)
    button.setText(name)
    button.clicked.connect(self.changeProject(name))
    setattr(self, "btn_%s" % name, button)

Answer 2

What the error message is telling you is that self.changeProject("%s") for one of the values you're substituting for that %s returns None. Presumably you meant for that method to return something different?

It's impossible to help you much with the task of debugging changeProject further without seeing the code for it, of course. However, you could for example split the call into something like (once you've gotten rid of that ton of execs as per lazy1's suggestion):

cp_result = self.changeProject(name)
if cp_result is None:
    logging.error('changeProject(%s) is None!', name)
else:
    logging.info('changeProject(%s) is OK (%r)', name, cp_result)
    button.clicked.connect(cp_result)

This way instead of uselessly trying to "connect to None", you'll see all the names causing that to-you-surprising return value in your error log, and can then continue debugging based on that information. However, more likely than not, your bug might in fact become obvious by looking at the source of changeProject.

Edit: the argument to connect is of course coming from changeProject (not from another connect!-) -- fixed the snippet accordingly.

Answer 3

I think you running 'exec' is too much, IMO. Your problem is that you are trying to connect to the QPushButton's .clicked(), which is really a signal. Do you really need to pass the argument here

exec 'self.btn_%s.clicked.connect(self.changeProject("%s"))' % (x, x)

Because if you don't you can connect it like this:

self.connect(self.btn_%s, SIGNAL('clicked()'), self.changeProject)

If you need to know which button is clicked you can iterate through the list to find which button is clicked:

for x in buttons:
if x.isDown(): (function)

You can also use pyqtSignal.

Answer 4

Thanks for the assistance. I stumbled QSignalMapper, and this turned out to be exactly what I needed.

http://pysnippet.blogspot.com/2010/06/qsignalmapper-at-your-service.html