How to obtain the set of all signals for a given widget?

Question

I am looking through the Qt documentation. Is there a quick and dirty way to get a list of all signals that a widget can emit.

For example (withPyQt):

allSignalsList = thisWidget.getSignals()

Alternatively, is there is a nice place on the new Qt5 API that shows all the signals for a given QObject?

ekhumoro · Accepted Answer · 2021-08-13T01:52:46.447

There's no built-in method for listing signals, but normal python object introspection will get the information fairly easily:

from PyQt5 import QtCore, QtWidgets

def get_signals(source):
    cls = source if isinstance(source, type) else type(source)
    signal = type(QtCore.pyqtSignal())
    for subcls in cls.mro():
        clsname = f'{subcls.__module__}.{subcls.__name__}'
        for key, value in sorted(vars(subcls).items()):
            if isinstance(value, signal):
                print(f'{key} [{clsname}]')

get_signals(QtWidgets.QPushButton)

Output:

clicked [PyQt5.QtWidgets.QAbstractButton]
pressed [PyQt5.QtWidgets.QAbstractButton]
released [PyQt5.QtWidgets.QAbstractButton]
toggled [PyQt5.QtWidgets.QAbstractButton]
customContextMenuRequested [PyQt5.QtWidgets.QWidget]
windowIconChanged [PyQt5.QtWidgets.QWidget]
windowIconTextChanged [PyQt5.QtWidgets.QWidget]
windowTitleChanged [PyQt5.QtWidgets.QWidget]
destroyed [PyQt5.QtCore.QObject]
objectNameChanged [PyQt5.QtCore.QObject]

However, it's probably better to learn to use the Qt Documentation. If you go to the page for a Qt class, there's a Contents sidebar on the top-right which has links for the main member types. This usually includes a section for signals, but if it doesn't, you can drill down through the inherited classes until you find one.

So for example, the QPushButton page doesn't show a signals section, but it inherits QAbstractButton, which does have one.

So for the classes that don't show signals on the 'contents' sidebar, you must look at the class from which it inherits. I see. Also, nice, instructive code snippet. — ADB, Feb 01 '15 at 07:21
Is there a safe way to detect and skip all signals originating from the QObject base? — Silicomancer, Aug 12 '21 at 22:47
@Silicomancer I updated the code example so that it breaks it down by class. Hopefully you can see how to adapt that to your own use-case. — ekhumoro, Aug 13 '21 at 01:55

score 7 · Answer 2 · answered Feb 01 '15 at 03:00

The trick is to use the QObject's meta object to iterate through the QObject's methods, then pick out the ones that have a signal type.

For example, this code snippet will print out the names of QThread's signals:

QThread thread;
QMetaObject metaObject = thread.staticMetaObject;
for (int i = 0; i < metaObject.methodCount(); i++) {
    QMetaMethod method = metaObject.method(i);
    if (method.methodType() == QMetaMethod::Signal) {
        qDebug() << "Signal: " << method.name();
    }
}

It should be trivial to adapt that to put the QMetaMethods into a QList or any other data structure.

How to obtain the set of all signals for a given widget?

2 Answers2