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"Latching" variables in function

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I've probably used the wrong term - I'm thinking of what I do when writing PLC code - so I can't find how to do this in my reference books.
This is part of a project I'm working on with a Raspberry Pi and an MCP23017 port expander.
I have a N/O pushbutton that I want to "latch" a value to a variable when it's been pressed.  I have this function that gets called periodically in
a 'while True' statement:


def button():
   pushbutton = 0
  button_value = 0
   pushbutton=bus.read_byte_data(address,GPIOB)
   if pushbutton > 0:
        button_value = 1
   return button_value




I need button_value to become '1' when the button is pressed and to remain '1' until the entire program (only about 25 lines) ends with a sys.exit()


What do I use to 'latch' button_value?




Brian Grawburg
North Carolina

-- 
The truth will set you free . . .but first it will infuriate you.

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"Latching" variables in function Grawburg <grawburg@myglnc.com> - 2014-04-08 16:09 -0400
  Re: "Latching" variables in function Denis McMahon <denismfmcmahon@gmail.com> - 2014-04-09 00:28 +0000
  Re: "Latching" variables in function Mark H Harris <harrismh777@gmail.com> - 2014-04-09 08:53 -0500
    Re: "Latching" variables in function alister <alister.nospam.ware@ntlworld.com> - 2014-04-09 15:43 +0000

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