Forever Loops

Video Tutorial

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Text Tutorial

In robotics, we always run our programs forever, using iteration, or a loop.

In this first tutorial, we’ll learn:

• What a Loop or “iteration” is.
• How loops differ from single line programs

Let’s try the difference between these 2 programs

Single Line Program

1. Connect the M4 to your computer, and load code.py
2. On line 1, write ` print(“this is a non-looped program)`
3. Open the serial console.
4. Save this program and observe the serial output

While True

1. delete all existing code.
2. write in this code:

import time

while True:
    print("this is in a loop!")
    time.sleep(1)

1. Open the serial console
2. Save this program and observe the serial output.

Examining a While True Loop:

You’ve likely noticed by now that rather than printing the statement once, it will print forever, in a loop! That’s what the “while True:” statement does. Let’s examine this:

• The word “while” is a condition for a loop. While the condition inside the following statement is true, the code “inside” the loop will continue to run. In our case, it will print “This is in a loop!” forever.
• The words next to the “while” are the conditional statement. We only ever run “True” statements:
  • while True: this will run because the statement is simply “True”
  • while 1 == 1: This will also run because 1 is equivalent to 1
  • while 5 == 7: This will never run, because 5 is not equal to 7.
• The last part of our conditional statement is the “:” colon. The colon signifies to our computer that the statement is over.
  • much like this indentation in the bullet, anything that is indented inside of the “while True:” statement will run. For example try to run the following code:
• The import time and time.sleep(1) are special lines from a “module” that allow us to put second pauses into our code.

import time

print("this is before the loop")
while True:
    print("this is inside the loop")
    print("Still inside the loop")
    time.sleep(1)
print("this is NOT indented, so it is outside the loop")
print("the statement directly above, and this statement, will NEVER print")

• The final 2 print statements will never print on our serial console, because they are after our forever, while True: loop.
• In python, indents (tabs or x4 spaces) keep track of what parts of code are inside loops, or conditional statements, and what are not.

Key Takeaways

All of our robotics programs will have a single while True: loop inside of them, and this is where all of our code will run. Much like a robot vacuum, we want our robot following instructions forever, until it is powered off.