[Tutor] what is the meaning of variable e

[wang yong]

Hi tutors,

I am a newb. Please bear with my simple question. Please refer to the code
as following. The question is: what is the special meaning of 'e' variable
in the class of 'Button'. The second one is how function 'dragEnterEvent'
and 'dropEvent' got executed with calling from class 'example'. Thanks a
lot for the help.

Best,

Yong

The code is here:
#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PyQt4 tutorial

This is a simple drag and
drop example.

author: Jan Bodnar
website: zetcode.com
last edited: December 2010
"""

import sys
from PyQt4 import QtGui

class Button(QtGui.QPushButton):

    def __init__(self, title, parent):
        super(Button, self).__init__(title, parent)

        self.setAcceptDrops(True)

    def dragEnterEvent(self, e):

        if e.mimeData().hasFormat('text/plain'):
            e.accept()
        else:
            e.ignore()

    def dropEvent(self, e):
        self.setText(e.mimeData().text())


class Example(QtGui.QWidget):

    def __init__(self):
        super(Example, self).__init__()

        self.initUI()

    def initUI(self):

        edit = QtGui.QLineEdit('', self)
        edit.setDragEnabled(True)
        edit.move(30, 65)

        button = Button("Button", self)
        button.move(190, 65)

        self.setWindowTitle('Simple Drag & Drop')
        self.setGeometry(300, 300, 300, 150)


def main():

    app = QtGui.QApplication(sys.argv)
    ex = Example()
    ex.show()
    app.exec_()


if __name__ == '__main__':
    main()
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