Python Forum

making a simple remote radio control program. radio listens for packets
and if none received, keep listening. Im needing it to check if transmitted strings
(onset and unset as custom string triggers) match as my "commands" to control
electrical relay on or off... and if they dont match my 2 commands (else) just decode
string as ascii text and print the text. cannot get it to recognize my elif lines...

while True:
    packet = rfm9x.receive()
    
    if packet is None:
        led.value = False
        print("Received nothing! Listening again...")
    elif packet is onset:
        print("its now on") 
    elif packet is unset:
        print("its now off") 
    else:
        led.value = True
        print("Received (raw bytes): {0}".format(packet))
        packet_text = str(packet, "ascii")

You should test "==" not "is". Is should only be used when you are testing if two objects are the same instance. Below I make two bytes. They are constructed of the same bytes, but they are different objects.

x = bytes('12345', 'utf-8')
y = bytes('12345', 'utf-8')
print(x, y, id(x), id(y), x is y, x == y)

Output:
b'12345' b'12345' 2409442857008 2409442857104 False True

x and y are equivalent, but they are not the same. x is y returns False and x == y returns True.
Just in case rfm9x.receive() returns str, the same is true for them.

x = ''.join(['a', 'b', 'c'])
y = ''.join(['a', 'b', 'c'])
print(x, y, id(x), id(y), x is y, x == y)

Output:
abc abc 3078969735600 3078969723888 False True

You may wonder why I constructed the strings as I did. The reason for using join instead of a string literal is Python is clever and tries to be efficient. This code does not create two str objects.

x = 'abc'
y = 'abc'
print(x, y, id(x), id(y), x is y, x == y)

Output:
abc abc 1811113886448 1811113886448 True True

In this example not only does x == y, but x is y. Notice that the object id for x and y are the same.

(Sep-04-2021, 05:39 PM)deanhystad Wrote: [ -> ]You should test "==" not "is". Is should only be used when you are testing if two objects are the same instance. Below I make two bytes. They are constructed of the same bytes, but they are different objects.
x = bytes('12345', 'utf-8')
y = bytes('12345', 'utf-8')
print(x, y, id(x), id(y), x is y, x == y)
Output:
b'12345' b'12345' 2409442857008 2409442857104 False True
x and y are equivalent, but they are not the same. x is y returns False and x == y returns True.
Just in case rfm9x.receive() returns str, the same is true for them.
x = ''.join(['a', 'b', 'c'])
y = ''.join(['a', 'b', 'c'])
print(x, y, id(x), id(y), x is y, x == y)
Output:
abc abc 3078969735600 3078969723888 False True
You may wonder why I constructed the strings as I did. The reason for using join instead of a string literal is Python is clever and tries to be efficient. This code does not create two str objects.
x = 'abc'
y = 'abc'
print(x, y, id(x), id(y), x is y, x == y)
Output:
abc abc 1811113886448 1811113886448 True True
In this example not only does x == y, but x is y. Notice that the object id for x and y are the same.

thanks for the == tip
this worked for me...

onset = bytes("onset", "utf-8")
unset = bytes("unset", "utf-8")

while True:
    packet = rfm9x.receive(timeout=5)
    
    if packet is None:
        led.value = False
        print("Received nothing! Listening again...")
    elif packet == onset:
            print("its on")
    elif packet == unset:
            print("its off")
    else:
        led.value = True
        print("Received (raw bytes): {0}".format(packet))
        packet = str(packet, "ascii")

javiopro

deanhystad

javiopro