On 04/08/2014 01:09 PM, Grawburg wrote:
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?
If I understand correctly, once 'bus.read_byte_data()' has returned a non-zero value, 'button' should continue returning
1 even if 'bus.read_byte_data()' later returns a 0?
There are a couple options for this:
- use a default paramater as static storage
def button(_latched=[0])
push_button = _latched[0]
if not push_button:
button_value = bus.read_byte_data(address, GPIOB)
if button_value > 0:
_latched[0] = push_button = 1
return push_button
- use a class
# implementation left as an exercise for the reader ;)
--
~Ethan~
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