Translate from C++ to PySide2: https://wiki.qt.io/Technical_FAQ#How_can_I_align_the_checkboxes_in_a_view.3F

main.py

from PySide2.QtCore import Qt, QSize, QRect, QEvent
from PySide2.QtWidgets import QStyledItemDelegate, QStyleOptionViewItem, QApplication, QStyle, QTableWidget, \
    QTableWidgetItem


class ItemDelegate(QStyledItemDelegate):
    def paint(self, painter, option, index):
        opt = QStyleOptionViewItem(option)
        if index.column() == 0:
            textMargin = QApplication.style().pixelMetric(QStyle.PM_FocusFrameHMargin) + 1
            newRect = QStyle.alignedRect(option.direction, Qt.AlignCenter,
                                         QSize(option.decorationSize.width() + 5,
                                               option.decorationSize.height()),
                                         QRect(option.rect.x() + textMargin, option.rect.y(),
                                               option.rect.width() - (2 * textMargin),
                                               option.rect.height()))
            opt.rect = newRect

        QStyledItemDelegate.paint(self, painter, opt, index)

    def editorEvent(self, event, model, option, index):
        flags = model.flags(index)
        if not (flags & Qt.ItemIsUserCheckable) or not (flags & Qt.ItemIsEnabled):
            return False
        value = index.data(Qt.CheckStateRole)

        if event.type() == QEvent.MouseButtonRelease:
            textMargin = QApplication.style().pixelMetric(QStyle.PM_FocusFrameHMargin) + 1
            checkRect = QStyle.alignedRect(option.direction, Qt.AlignCenter,
                                           option.decorationSize,
                                           QRect(option.rect.x() + (2 * textMargin),
                                                 option.rect.y(),
                                                 option.rect.width() - (2 * textMargin),
                                                 option.rect.height()))
            if not checkRect.contains(event.pos()):
                return False

        elif event.type() == QEvent.KeyPress:
            if event.key() != Qt.Key_Space and event.key() != Qt.Key_Select:
                return False
        else:
            return False

        state = Qt.Unchecked if value == Qt.Checked else Qt.Checked
        return model.setData(index, state, Qt.CheckStateRole)


class Table(QTableWidget):
    def __init__(self):
        QTableWidget.__init__(self, 3, 1)
        self.setItemDelegate(ItemDelegate(self))
        for i in range(self.rowCount()):
            for j in range(self.columnCount()):
                it = QTableWidgetItem()
                self.setItem(i, j, it)
                it.setFlags(Qt.ItemIsEnabled | Qt.ItemIsUserCheckable)
                it.setCheckState(Qt.Checked if (i + j) % 2 == 0 else Qt.Unchecked)


if __name__ == '__main__':
    import sys

    app = QApplication(sys.argv)
    w = Table()
    w.show()
    sys.exit(app.exec_())

Thanks for this code snippet.
Would you know how to remove the weird thing on the right side of the active cell?

@sharpordie try with this code:

from PySide2.QtCore import Qt
from PySide2.QtWidgets import (
    QApplication,
    QProxyStyle,
    QStyle,
    QTableWidget,
    QTableWidgetItem,
)


class ProxyStyle(QProxyStyle):
    def subElementRect(self, e, opt, widget):
        r = super().subElementRect(e, opt, widget)
        if e == QStyle.SE_ItemViewItemCheckIndicator:
            r.moveCenter(opt.rect.center())
        return r


class Table(QTableWidget):
    def __init__(self):
        QTableWidget.__init__(self, 3, 1)
        self._style = ProxyStyle(self.style())
        self.setStyle(self._style)
        for i in range(self.rowCount()):
            for j in range(self.columnCount()):
                it = QTableWidgetItem()
                self.setItem(i, j, it)
                it.setFlags(Qt.ItemIsEnabled | Qt.ItemIsUserCheckable)
                it.setCheckState(Qt.Checked if (i + j) % 2 == 0 else Qt.Unchecked)


if __name__ == "__main__":
    import sys

    app = QApplication(sys.argv)
    w = Table()
    w.show()
    sys.exit(app.exec_())

Sorry for the HUGE delay.
Thank you very much, it's working perfectly.