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for j in range(z):

GPIO.output(LED[j], False)

time.sleep(t)

elif e == "5":

for i in range(w*z):

j = random.randint(0,z-1)

GPIO.output(LED[j], True); time.sleep(t)

GPIO.output(LED[j], False)

else:

print (“Invalid entry")

except KeyboardInterrupt:

GPIO.cleanup()

5.1.1 How does it work?

Through previous experiments you are already familiar with the first lines of the program that is, the

definition of the UTF-8 encoding and the import of the necessary libraries. Here, also the library

randomis

imported to generate a random blinking pattern.

We have taken care when developing this programme that it is versatile and can be used in many ways,

namely, that it easily possible to add more than only four LEDs. Today good programming practice embraces

such flexibility. Using the example of the Raspberry Pi, such coded applications can not only be broadened

by adding new GPIO ports, but it is also easy to rewrite them for other GPIO ports, should it be required by

some hardware technicalities.

LED = [4,18,23,24] Again a list of GPIO port numbers for the LEDs is defined, so that these ports are

recorded only once in the programmr.

for i in LED:

GPIO.setup(i, GPIO.OUT, initial=0)

Unlike earlier programmes where the GPIO ports of the LEDs were individually initialized, we will run a for

loop across the list of

LED this time. The loop counter i accepts each value from the list in succession, in our

example, the GPIO port numbers of LEDs, and is not simply incremented as in the previously used

for

loops.. Lists of any size can thus be processed. The length of the list may not even be known when the

programme is being developed.

The four GPIO ports are defined as outputs for the LEDs and are set to

0 so that any LEDs that may still be lit

as a result of previous experiments are disabled.

z = len(LED); w = 5; t = 0.2