Why is my Tk button being pressed automatically?

Question

In the code below, clicking the button should change the black text from Hello to Goodbye. But when I run the program, it immediately says Goodbye.

Answer 1

Because you are calling self.bpress when you create the self.button1 button:

self.button1 = Button(self, text = "Click Me", width = 10, command = self.bpress())
#                                                                               ^^

Simply remove the parenthesis and assign command to the self.bpress function object itself:

self.button1 = Button(self, text = "Click Me", width = 10, command = self.bpress)

Answer 2

For future reference:

If you want to send parameters to the function, simply add lambda:

Example for a button with the command callback():

yourButton = Tkinter.Button(root, text="Go!", command= lambda: callback(variableOne, variableTwo, variableThree)).pack()