import numpy as np
import pyqtgraph as pg
from pyqtgraph.Qt import QtCore, QtGui, QtWidgets

class ObjectBounds(QtWidgets.QGraphicsItem):
    def paint(self, painter, *args):
        pen = QtGui.QPen(QtCore.Qt.GlobalColor.red, 0, QtCore.Qt.PenStyle.DashLine)
        rect = self.boundingRect()
        painter.setPen(pen)
        painter.drawRect(rect)
        print(rect)

    def boundingRect(self):
        return self.parentItem().boundingRect()

pg.mkQApp()
pw = pg.PlotWidget()
pw.show()

rng = np.random.default_rng()
vals = np.hstack([rng.normal(size=500), rng.normal(size=260, loc=4)])
y,x = np.histogram(vals, bins=np.linspace(-3, 8, 40))

pen = pg.mkPen('w', width=6)
bgi = pg.BarGraphItem(x0=x[:-1], x1=x[1:], height=y, pen=pen, brush=(0,0,255,150))
pw.addItem(bgi)
rect = ObjectBounds(bgi)

pg.exec()