https://github.com/stlehmann/PyQt5-stubs/blob/189a0497d08ddd65f46e4819f427eb2d03196589/PyQt5-stubs/QtCore.pyi#L31 See this link: https://stackoverflow.com/questions/45337136/qsignalmapper-in-pyqt5-not-working-when-the-function-argument-is-a-str We're expected to do: "mapper.mapped[str].connect(a_function)" in order to retrieve the overload we want for the signal. It should be enough if we add __getitem__ returning pyqtSignal.