import sys

from PyQt5.QtWidgets import QMainWindow, QMenu, QAction, QApplication
from PyQt5.QtCore import Qt, pyqtSlot


class MainWindow(QMainWindow):

    def __init__(self):
        super().__init__()

        self.setContextMenuPolicy(Qt.CustomContextMenu)
        self.customContextMenuRequested.connect(self.on_content_menu)

    def on_content_menu(self, pos):
        context = QMenu(self)
        context.addAction(QAction("test1", self))
        context.addAction(QAction("test2", self))
        context.addAction(QAction("test3", self))
        context.exec_(self.mapToGlobal(pos))


app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec_())