self.ui.PoseBtn_GridLayout.setColumnMinimumWidth(4, 4)
spacerItem = QtGui.QSpacerItem(40, 20, QtGui.QSizePolicy.Expanding, QtGui.
    QSizePolicy.Minimum)
self.ui.PoseBtn_GridLayout.addItem(spacerItem, 1, 1, 1, 1)
spacerItem1 = QtGui.QSpacerItem(20, 40, QtGui.QSizePolicy.Minimum, QtGui.
    QSizePolicy.Expanding)
self.ui.PoseBtn_GridLayout.addItem(spacerItem1, 1, 0, 1, 1)
self.button = QtGui.QPushButton('')
self.button.setIcon(self._icon)
self.button.setIconSize(QtCore.QSize(128, 128))
self.button.setMinimumSize(QtCore.QSize(128, 128))
self.button.setMaximumSize(QtCore.QSize(128, 128))
self.ui.PoseBtn_GridLayout.addWidget(self.button, 0, 0, 1, 1)
How to add widget to gridlayout starting from top-left corner