checkable combobox with autocomplete

[Gabriel_xyz]

Hello everyone!
I'm trying to implement a combobox with checkable items, so the user can multi-select, and search.

Here is the code:

from PyQt5.QtWidgets import QApplication, QComboBox, QCompleter, QLineEdit
from PyQt5.QtCore import Qt

class CheckableComboBox(QComboBox):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setEditable(True)
        self.setInsertPolicy(QComboBox.NoInsert)

        # Make Completer for Search Box
        self.completer = QCompleter()
        self.completer.setFilterMode(Qt.MatchContains)
        self.completer.setCaseSensitivity(Qt.CaseInsensitive)

        # Make Search Box for Combo Box
        self.search_box = QLineEdit()
        self.search_box.setCompleter(self.completer)
        self.search_box.setFocus()
        self.search_box.selectAll()

        self.setLineEdit(self.search_box)
        self.completer.setModel(self.model())


if __name__ == '__main__':
    app = QApplication([])
    region = ['South', 'North', 'East', 'West']
    combo = CheckableComboBox()
    combo.addItems(region)
    combo.show()
    model = combo.model()
    app.exec()

The checkboxes are being displayed, but the auto-compete does not work.

Any advice would be much appreciated!