Learning about Python and R_PI

I decided to try one of the learn modules on the Raspberry Pi web site. This introduces me to

1 Python3

2 Using the GPIO pins

I wired up the 10 LEDs as shown on the R_PI project page. Then started Menu > Programming > Python 3. The first window is raw access to the Python interpreter, here you can type commands and see them happen. To create an app you need to open File > New File in a new window, here you can type your program. You must save it, so I suggest to go out to the File Manager and create a new folder under Documents > Python3 Projects. Then you can save you work there.

The program looks like this:

import requests
from gpiozero import LED

pins = [2, 3, 4, 14, 15, 17, 18, 27, 23, 22]
leds = [LED(p) for p in pins]

url = "http://api.open-notify.org/astros.json"

r = requests.get(url)
j = r.json()
n = j['number']

for i, led in enumerate(leds):
    if n > i:
        led.on()
    else:
        led.off()

I saved it as astros.py. Run it by Run > Run Module. And if you got it all wired up right and typed in right, at this moment there are 6 astronauts on the ISS so 6 LEDs will light up.

As I understand it the program works like this

- import the libraries you need "requests" and the "gpiozero" function "LED".

- define a list of the led pins you have wired up

- make another list from this of the leds you will access and their pin numbers

- define the url for the data and get the data from it into variable "r"

- read the json data into the variable "j"

- finally extract the 'number' of astronauts from the json "number" data

- enumerate the leds - simply number them 0...9. And step through them in a "for" loop. If the number of astronauts "n" is more than the current led "i" in the loop, turn it on. Else turn it off.

This will give 6 LEDs on for 6 astronauts.