import sys
from PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication
class Example(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()
    def initUI(self):
        self.btn1 = QPushButton("Button 1", self)
        self.btn1.move(10, 30)
        self.btn2 = QPushButton("Button 2", self)
        self.btn2.move(115, 30)
        self.btn3 = QPushButton("Button 3", self)
        self.btn3.move(220, 30)
        self.btn4 = QPushButton("Ren", self)
        self.btn4.move(115, 80)
        self.btn4.clicked.connect(self.buttonClicked)
        self.setGeometry(300, 300, 330, 150)
        self.setWindowTitle('buttons')
        self.show()
    def buttonClicked(self):
        self.btn1.setText("Name1")
        self.btn2.setText("Name2")
        self.btn3.setText("Name3")
if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

  import sys
from PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication
class Example(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()
    def initUI(self):
        self._btns = []
        for i in range (3):
            self._btns.append(QPushButton("Button {}".format(i+1) , self))
            self._btns[i].move(i+10+i*100, 30)
        
        self.btn_rename = QPushButton("Ren", self)
        self.btn_rename.move(115, 80)
        self.btn_rename.clicked.connect(self.buttonClicked)
        self.setGeometry(300, 300, 330, 150)
        self.setWindowTitle('buttons')
        self.show()
    def buttonClicked(self):
        for i, btn in enumerate(self._btns):
            btn.setText("Name{}".format(i+1))
if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())