Get clicked chess piece from an SVG chessboard

I am developing a chess GUI in Python 3.6.3 using PyQt5 5.9.1 (GUI framework) and python-chess 0.21.1 (chess library) on Windows 10. I want to get the value of a piece that was clicked on an SVG chessboard (provided by python-chess) so that I can then move that piece to another square.

After the first left mouse click and getting the piece, I want to get the second left mouse click from the user and get the square that the user clicked on. Then my chess GUI must move the piece from originating square to the target square.

So, here's my complete working code so far. Any hints or actual code additions are very welcome.

import chess
import chess.svg
from PyQt5.QtSvg import QSvgWidget
from PyQt5.QtCore import pyqtSlot, Qt
from PyQt5.QtWidgets import QApplication, QWidget


class MainWindow(QWidget):
    def __init__(self):
        super().__init__()

        self.setWindowTitle("Chess Titan")
        self.setGeometry(300, 300, 800, 800)

        self.widgetSvg = QSvgWidget(parent=self)
        self.widgetSvg.setGeometry(10, 10, 600, 600)

        self.chessboard = chess.Board()

    @pyqtSlot(QWidget)
    def mousePressEvent(self, event):
        if event.buttons() == Qt.LeftButton:
            ## How to get the clicked SVG chess piece?

            # Envoke the paint event.
            self.update()

    @pyqtSlot(QWidget)
    def paintEvent(self, event):
        self.chessboardSvg = chess.svg.board(self.chessboard).encode("UTF-8")
        self.widgetSvg.load(self.chessboardSvg)


if __name__ == "__main__":
    chessTitan = QApplication([])
    window = MainWindow()
    window.show()
    chessTitan.exec()

If size of chessboard is known, you can find the coordinates of the mouseclick from event.pos() resp.event.x(), event.y() depending on marginwidth and squaresize, see chess.svg.py line 129 ff.

edit Nov 25: event.pos() is in this example in MainWindow coordinates, to find the coordinates on chessboard all must be calculated from top left corner represented by self.svgX and self.svgY:

import chess
import chess.svg
from PyQt5.QtCore import pyqtSlot, Qt
from PyQt5.QtSvg import QSvgWidget
from PyQt5.QtWidgets import QApplication, QWidget


class MainWindow(QWidget):
    def __init__(self):
        super().__init__()

        self.setWindowTitle("Chess Titan")
        self.setGeometry(300, 300, 800, 800)

        self.widgetSvg = QSvgWidget(parent=self)
        self.svgX = 50                          # top left x-pos of chessboard
        self.svgY = 50                          # top left y-pos of chessboard
        self.cbSize = 600                       # size of chessboard
        self.widgetSvg.setGeometry(self.svgX,self.svgY, self.cbSize, self.cbSize)
        self.coordinates = True
        # see chess.svg.py line 129
        self.margin = 0.05*self.cbSize if self.coordinates == True else 0
        self.squareSize  = (self.cbSize - 2 * self.margin) / 8.0
        self.chessboard = chess.Board()
        self.pieceToMove = [None, None]

    @pyqtSlot(QWidget)
    def mousePressEvent(self, event):
        if self.svgX < event.x() <= self.svgX + self.cbSize and self.svgY < event.y() <= self.svgY + self.cbSize:   # mouse on chessboard
            if event.buttons() == Qt.LeftButton:
                # if the click is on chessBoard only
                if self.svgX + self.margin < event.x() < self.svgX + self.cbSize - self.margin and self.svgY + self.margin < event.y() < self.svgY + self.cbSize - self.margin:
                    file = int((event.x() - (self.svgX + self.margin))/self.squareSize)             
                    rank = 7 - int((event.y() - (self.svgY + self.margin))/self.squareSize) 
                    square = chess.square(file, rank)                       # chess.sqare.mirror() if white is on top
                    piece = self.chessboard.piece_at(square)
                    coordinates = '{}{}'.format(chr(file + 97), str(rank +1))       
                    if self.pieceToMove[0] is not None:
                        move = chess.Move.from_uci('{}{}'.format(self.pieceToMove[1], coordinates))
                        self.chessboard.push(move)
                        print(self.chessboard.fen())
                        piece = None
                        coordinates= None
                    self.pieceToMove = [piece, coordinates]                                           
                else:
                    print('coordinates clicked')
                # Envoke the paint event.
                self.update()
        else:
            QWidget.mousePressEvent(self, event)

    @pyqtSlot(QWidget)
    def paintEvent(self, event):
        self.chessboardSvg = chess.svg.board(self.chessboard, size = self.cbSize, coordinates = self.coordinates).encode("UTF-8")
        self.widgetSvg.load(self.chessboardSvg)


if __name__ == "__main__":
    chessTitan = QApplication([])
    window = MainWindow()
    window.show()
    chessTitan.exec()

move white and black pieces alternating, they change the color if the same color is moved twice.