PyQt4.QtCore.pyqtSignal object has no attribute 'connect'

Question

I'm having issues with a custom signal in a class I made.

Relevant code:

self.parse_triggered = QtCore.pyqtSignal()

def parseFile(self):
    self.emit(self.parse_triggered)

Both of those belong to the class: RefreshWidget. In its parent class I have:

self.refreshWidget.parse_triggered.connect(self.tabWidget.giveTabsData())

When I try to run the program, I get the error:

AttributeError: 'PyQt4.QtCore.pyqtSignal' object has no attribute 'connect'

Help? Thanks in advance.

Answer 1

I had the same exact problem as you.

Try moving

self.parse_triggered = QtCore.pyqtSignal()

out of your constructor but inside your class declaration. So instead of it looking like this:

class Worker(QtCore.QThread):
    def __init__(self, parent = None):
        super(Worker, self).__init__(parent)

        self.parse_triggered = QtCore.pyqtSignal()

It should look like this:

class Worker(QtCore.QThread):
    parse_triggered = QtCore.pyqtSignal()

    def __init__(self, parent = None):
        super(Worker, self).__init__(parent)

This might not be at all what you are looking for, but it worked for me. I switched back to old-style signals anyways because I haven't found a way in new-style signals to have an undefined number or type of parameters.

Answer 2

You also get that error message if you fail to call super() or QObject.__init__() in your custom class.

A checklist for defining custom signals in a class in Qt in Python:

• your class derives from QObject (directly or indirectly)
• your class __init__ calls super() (or calls QObject.__init__() directly.)
• your signal is defined as a class variable, not an instance variable
• the signature (formal arguments) of your signal matches the signature of any slot that you will connect to the signal e.g. () or (int) or (str) or ((int,), (str,))

Answer 3

I have recently started working with PySide (Nokia's own version of PyQt), and saw the exact same behaviour (and solution) with custom new-style signals. My biggest concern with the solution was that using a class variable to hold the signal would mess things up when I have multiple instances of that class (QThreads in my case).

From what I could see, QtCore.QObject.__init__(self) finds the Signal variable in the class and creates a copy of that Signal for the instance. I have no idea what QObject.__init__() does, but the resulting Signal does proper connect(), disconnect() and emit() methods (and also a __getitem__() method), whereas the class Signal or standalone Signal variables created outside of a QObject-derived class do not have these methods and can't be used properly.