SVA-CS2-24

Python Crash Course

CircuitPython is based on MicroPython which is a slimmed down version of… you guessed it, python! Here are some python basics to get you started.

Variables

Here is how you set variables.

age = 39

Here, age is the name of the variable and 39 is a number value that gets assigned to the variable.

Here is another example, using text.

name = "Adam"

If Statements

One thing to know about python is white space (spaces and tabs) is important in python. There are no curly braces here. You use white space to show where a block of code begins and end.

Here is a super simple example, notice how the print command is indented.

age = 39

if age >= 18:
  print("you can buy a lotto ticket now!")

Lets add another conditional:

age = 22

if age >= 21:
  print("you can buy alcohol!")
else:
  print("it's ok, drinking is overrated.")

And here is one last conditional, with many options:

age = 19

if age >= 21:
  print("full adult rights")
elif age >= 18:
  print("you can vote and gamble")
else:
  print("you'll grow up some day!)

While Loops

While loop will run while a condition is true. This code will print “hello” six times.

i = 0
while i < 6:
  print("hello")
  i += 1

Generally, we want to avoid continuous loops, but on a microcontroller, we often want our code to run forever, so you might see a ‘forever loop’ that looks like this.

while True:
  print("running")

Anything inside the while loop will run forever. Ctrl-D in the mu editor will halt the code.

For loops

We can use a for loop to run a block of code a certain amount of times. This code does exactly the same output as the first while statement above.

for x in range(6):
  print("hello")

Here, we are looping over a range of values from 0 to 6.

In python, it is easy to loop over an array of values.

fruits = ["apple", "banana", "cranberry", "date"]
for fruit in fruits:
  print(fruit)

Functions

We can write functions to make our code neat, organized, and repeatable. You define a function with the def keyword.

def hello():
  print("hello")

And then we can call the function with hello()

A function can take in any number of values as parameters:

def hello(name):
  print("hello " + name + "!")

Now we can greet specific people, hello("adam")

Circuit Python “Hello World”

Let’s look again at a simple CircuitPython “Hello World” flashy program, this time with comments.

"""Example for Pico. Turns the built-in LED on and off with no delay."""
# import the time module form python core 
import time

# import different modules from circuitpython
import board
import digitalio

# assign the variable led to the boards led 
led = digitalio.DigitalInOut(board.LED) 
led.direction = digitalio.Direction.OUTPUT # set to output data.

while True: # forever loop
    led.value = True # turn the led on
    time.sleep(0.5) # delay half a second, keeps the led on
    led.value = False # turn the led off
    time.sleep(0.5) # delay, keeps the led off before repeat, otherwise it won't look like it ever turns off

There is a lot more to learn here! Check out this resources to start your journey.

Resource