ScrollArea

import sys

from PyQt5 import QtWidgets, QtCore

class ScrollArea(QtWidgets.QScrollArea):
    def __init__(self, parent = None):
        super().__init__(parent)
        self._buttons = []
        widget = QtWidgets.QWidget()
        layout = QtWidgets.QVBoxLayout()
        widget.setLayout(layout)
        self.setWidget(widget)
        self.setWidgetResizable(True)

    def addButton(self):
        index = len(self._buttons)
        text = "button {}".format(index)
        button = QtWidgets.QPushButton(text)
        self.widget().layout().addWidget(button)
        self._buttons.append(button)
        button.clicked.connect(self.addButton)
        return button

if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    widget = ScrollArea()
    QtCore.QTimer.singleShot(0, lambda: widget.addButton())
    QtCore.QTimer.singleShot(0, lambda: widget.addButton())
    widget.show()
    exit(app.exec_())