Как построить график matplotlib в widget по данным из tableWidget?

Можно так:

import random
import numpy as np
from PyQt5 import QtCore, QtGui, QtWidgets

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar
from matplotlib.figure import Figure


#from untitled import Ui_MainWindow
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(640, 480)
# ???        MainWindow.setStyleSheet("QWidget{\n"
# ???"Width: 200px;\n"
# ???"Heigth: 250px;\n"
# ???"}")
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.gridLayout_2 = QtWidgets.QGridLayout(self.centralwidget)
        self.gridLayout_2.setObjectName("gridLayout_2")
        self.tabWidget = QtWidgets.QTabWidget(self.centralwidget)
        self.tabWidget.setObjectName("tabWidget")
        self.tab = QtWidgets.QWidget()
        self.tab.setObjectName("tab")
        self.gridLayout = QtWidgets.QGridLayout(self.tab)
        self.gridLayout.setObjectName("gridLayout")
        self.tableWidget = QtWidgets.QTableWidget(self.tab)
        self.tableWidget.setObjectName("tableWidget")
        self.tableWidget.setColumnCount(5)
        self.tableWidget.setRowCount(5)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setVerticalHeaderItem(0, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setVerticalHeaderItem(1, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setVerticalHeaderItem(2, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setVerticalHeaderItem(3, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setVerticalHeaderItem(4, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setHorizontalHeaderItem(0, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setHorizontalHeaderItem(1, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setHorizontalHeaderItem(2, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setHorizontalHeaderItem(3, item)
        item = QtWidgets.QTableWidgetItem()
        self.tableWidget.setHorizontalHeaderItem(4, item)
        self.gridLayout.addWidget(self.tableWidget, 0, 0, 1, 1)
        self.pushButton = QtWidgets.QPushButton(self.tab)
        self.pushButton.setObjectName("pushButton")
        self.gridLayout.addWidget(self.pushButton, 1, 0, 1, 1)
        self.tabWidget.addTab(self.tab, "")
        
        self.tab_2 = QtWidgets.QWidget()
        self.tab_2.setObjectName("tab_2")
        self.gridLayout_3 = QtWidgets.QGridLayout(self.tab_2)
        self.gridLayout_3.setObjectName("gridLayout_3")
        self.widget = QtWidgets.QWidget(self.tab_2)
        self.widget.setObjectName("widget")
       
        self.gridLayout_3.addWidget(self.widget, 0, 0, 1, 1)
        self.tabWidget.addTab(self.tab_2, "")
        
        self.gridLayout_2.addWidget(self.tabWidget, 2, 0, 1, 1)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 640, 21))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        self.tabWidget.setCurrentIndex(1)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        item = self.tableWidget.verticalHeaderItem(0)
        item.setText(_translate("MainWindow", "1"))
        item = self.tableWidget.verticalHeaderItem(1)
        item.setText(_translate("MainWindow", "2"))
        item = self.tableWidget.verticalHeaderItem(2)
        item.setText(_translate("MainWindow", "3"))
        item = self.tableWidget.verticalHeaderItem(3)
        item.setText(_translate("MainWindow", "4"))
        item = self.tableWidget.verticalHeaderItem(4)
        item.setText(_translate("MainWindow", "5"))
        item = self.tableWidget.horizontalHeaderItem(0)
        item.setText(_translate("MainWindow", "1"))
        item = self.tableWidget.horizontalHeaderItem(1)
        item.setText(_translate("MainWindow", "2"))
        item = self.tableWidget.horizontalHeaderItem(2)
        item.setText(_translate("MainWindow", "3"))
        item = self.tableWidget.horizontalHeaderItem(3)
        item.setText(_translate("MainWindow", "4"))
        item = self.tableWidget.horizontalHeaderItem(4)
        item.setText(_translate("MainWindow", "5"))
        self.pushButton.setText(_translate("MainWindow", "График"))
        self.tabWidget.setTabText(self.tabWidget.indexOf(self.tab), _translate("MainWindow", "Tab 1"))
        self.tabWidget.setTabText(self.tabWidget.indexOf(self.tab_2), _translate("MainWindow", "Tab 2"))


class MyMplCanvas(FigureCanvas):
    def __init__(self, *args, **kwargs):
        self.fig = Figure()
        super(MyMplCanvas, self).__init__(self.fig, *args, **kwargs)

    def plot(self, labels, men_means, women_means, x, width):          
        self.fig.clear()                                                   
        self.ax = self.fig.add_subplot(111)                                
        rects1 = self.ax.bar(x - width/2, men_means, width, label='Men')
        rects2 = self.ax.bar(x + width/2, women_means, width, label='Women')
        self.ax.set_ylabel('Scores')
        self.ax.set_title('Scores by group and gender')
        self.ax.set_xticks(x)
        self.ax.set_xticklabels(labels)
        self.ax.legend()
        self.draw()                                                    


class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        
        self.tabWidget.setCurrentIndex(0)
        self.pushButton.clicked.connect(self.chart)
        
        self.canvas = MyMplCanvas()
        self.toolbar = NavigationToolbar(self.canvas, self)
        self.layout = QtWidgets.QVBoxLayout(self.widget)
        self.layout.addWidget(self.canvas)   
        self.layout.addWidget(self.toolbar)
        self.toolbar.hide()                   

    def chart(self):
        rows = self.tableWidget.rowCount()
        
        men_means = []
        women_means = []
        for row in range(rows): 
            item = self.tableWidget.item(row, 0)
            item = item.text() if item else '0'
            men_means.append(float(item) if item else 0)  
            item = self.tableWidget.item(row, 1)
            item = item.text() if item else '0'
            women_means.append(float(item) if item else 0) 

        labels = ['G1', 'G2', 'G3', 'G4', 'G5']
        x = np.arange(len(labels))          
        width = 0.35                               
        self.canvas.plot(labels, men_means, women_means, x, width)    
        self.toolbar.show()                    
        
        self.tabWidget.setCurrentIndex(1)
        
    
if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())