Pyqt5 中方法后面的按钮不可见

我是新手，对这一切还不是很熟悉，所以如果没有必要的信息给你，我很抱歉。
按钮 ( quadratic) 不仅在方法中定义，而且无法访问。

    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(1000, 700)
        font = QtGui.QFont()
        font.setPointSize(15)
        MainWindow.setFont(font)
        MainWindow.setStyleSheet("background-color: #2E4172")
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.quadratic = QtWidgets.QPushButton(self.centralwidget)

    def choice(self):  # choice btn's
        self.quadratic.clicked.connect(lambda: self.output_qua())
        self.linear.clicked.connect(lambda: self.show_dif())

这是错误：

AttributeError：“Ui_MainWindow”对象没有“二次”属性。

提前致谢

更新：

例子

# -*- coding: utf-8 -*-
import sys
from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def __init__(self):
        self.click_event()

    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(300, 180, 221, 111))
        self.pushButton.setObjectName("pushButton")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 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)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))

    def click_event(self):
        self.pushButton.clicked.connect(lambda: self.f())

    def f(self):
        self.pushButton.hide()


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())