解决了布局问题1和布局问题2，接下来，你的Main函数如果写成下面这样，直接运行，什么也不会显示？

> if __name__=='__main__':
  app = QApplication(sys.argv)
  MainWindow = QMainWindow()
  ui = Ui_MainWindow()
  ui.setupUi(MainWindow)
  MainWindow.show()
  app.exec()

什么也不会显示

如果你不想修改main中的内容，必须在class Ui_MainWindow(QWidget) 类中添加一个初始化方法就可以了：

def __init__(self):
     super().__init__()
     self.setupUi(MainWindow)

完整代码如下：

import sys
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtWidgets import QApplication,QMainWindow,QWidget


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

    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayoutWidget = QtWidgets.QWidget(self.centralwidget)
        self.verticalLayoutWidget.setGeometry(QtCore.QRect(230, 130, 160, 112))
        self.verticalLayoutWidget.setObjectName("verticalLayoutWidget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.verticalLayoutWidget)
        self.verticalLayout.setContentsMargins(0, 0, 0, 0)
        self.verticalLayout.setObjectName("verticalLayout")
        self.pushButton = QtWidgets.QPushButton(self.verticalLayoutWidget)
        self.pushButton.setObjectName("pushButton")
        self.verticalLayout.addWidget(self.pushButton)
        self.pushButton_2 = QtWidgets.QPushButton(self.verticalLayoutWidget)
        self.pushButton_2.setObjectName("pushButton_2")
        self.verticalLayout.addSpacing(10)
        # 在按钮1 和 按钮2 之间增加距离10
        self.verticalLayout.addSpacing(10)
        self.verticalLayout.addWidget(self.pushButton_2)
        self.pushButton_3 = QtWidgets.QPushButton(self.verticalLayoutWidget)
        self.pushButton_3.setObjectName("pushButton_3")
        self.verticalLayout.addWidget(self.pushButton_3)
        self.pushButton_4 = QtWidgets.QPushButton(self.verticalLayoutWidget)
        self.pushButton_4.setObjectName("pushButton_4")
        self.verticalLayout.addWidget(self.pushButton_4)
        self.setLayout(self.verticalLayout)

        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 23))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")

        MainWindow.setStatusBar(self.statusbar)
        # 设置垂直布局间距为10
        self.verticalLayout.setSpacing(10)
        self.setLayout(self.verticalLayout)
        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", "1"))
        self.pushButton_2.setText(_translate("MainWindow", "2"))
        self.pushButton_3.setText(_translate("MainWindow", "3"))
        self.pushButton_4.setText(_translate("MainWindow", "4"))

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

以上代码运行的效果如下：