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>>> from PyQt5.QtCore import QObject, pyqtSignal
>>> obj = QObject()
>>> sig = pyqtSignal()
>>> obj.emit(sig)
Traceback (most recent call last):
  File"<stdin>", line 1, in <module>
AttributeError: 'QObject' object has no attribute 'emit'

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>>> obj.sig.emit()
Traceback (most recent call last):
  File"<stdin>", line 1, in <module>
AttributeError: 'QObject' object has no attribute 'sig'

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>>> obj.sig = pyqtSignal()
>>> obj.sig.emit()
Traceback (most recent call last):
  File"<stdin>", line 1, in <module>
AttributeError: 'PyQt5.QtCore.pyqtSignal' object has no attribute 'emit'

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from PyQt5.QtCore import QObject, pyqtSignal

class Foo(QObject):

    # Define a new signal called 'trigger' that has no arguments.
    trigger = pyqtSignal()

    def connect_and_emit_trigger(self):
        # Connect the trigger signal to a slot.
        self.trigger.connect(self.handle_trigger)

        # Emit the signal.
        self.trigger.emit()

    def handle_trigger(self):
        # Show that the slot has been called.

        print"trigger signal received"