Control#

Introduction#

Control in Python lets you tell the robot when to wait, when to repeat actions, how to make decisions, and when to end the project.

Below is a list of all controls, including methods and core Python keywords:

  • wait – Pauses the project for a given time.

  • for – Repeats code for each item in a sequence.

  • if – Runs code if a condition is true.

  • if/else – Runs different code depending on a condition.

  • if/elif/else – Checks multiple conditions in order.

  • while – Repeats code while a condition is true.

  • break – Exits a loop immediately.

  • stop_program – Ends the running program.

  • pass – Placeholder used when no action is needed.

Wait#

wait pauses for a specific amount of time before moving to the next line of code.

Usage:
wait(time, units)

Parameters

Description

time

The amount of time to wait, as a positive whole number or decimal.

units

The unit that represents the wait time: MSEC (default) – milliseconds, or SECONDS

 
# Move right for one second, then stop
robot.move_at(90)
wait(1, SECONDS)
robot.stop_all_movement()

For#

for repeats a set of actions a specific number of times. for can be used to loop through items in lists, tuples, dictionaries, sets, strings, or for a specified amount of loops with range.

Usage:

for value in expression_list:
    pass

Components

Description

value

A temporary variable that stores the current element in the iteration.

expression_list

The collection of elements being looped through (e.g., list, string, range).

 
# Move in a square path.
for index in range(4):
    robot.move_for(50, 0)
    robot.turn_for(RIGHT, 90)


# Print each item in the list
colors = ["Red", "Green", "Blue"]

for color in colors:
    robot.screen.print(color)
    robot.screen.next_row()

Displays three objects being printed on the screen.

If#

if runs the indented block of code if the condition is True.

Usage:

if condition:
    pass

Components

Description

condition

An expression or variable that is checked when the statement runs. If it is True, the code inside the if block executes; if it is False, the block is skipped.

 
# Kick when the screen is pressed
while True:
    if robot.screen.pressing():
        robot.kicker.kick(MEDIUM)
    wait(0.1, SECONDS)

If/Else#

if and else determine which indented block of code runs based on whether the condition is True or False.

Usage:

if condition:
    pass
else:
    pass

Components

Description

condition

An expression or variable that is checked when the statement runs. If it is True, the code inside the if block executes; if it is False, the code inside the else block executes instead.

 
# Show one emoji when the screen is pressed,
# and a different emoji when not pressed
while True:
    if robot.screen.pressing():
        robot.screen.show_emoji(EXCITED)

    else:
        robot.screen.show_emoji(BORED)
    
    wait(0.1, SECONDS)

If/Elif/Else#

The if/elif/else structure selects which indented block of code runs based on conditions:

  • if runs its block if the condition is True.

  • elif checks additional conditions only if all previous conditions are False. Multiple elif statements can be used.

  • else runs its block only if none of the previous conditions are True.

Usage:

if condition:
    pass
elif condition:
    pass
else:
    pass

Components

Description

condition

An expression or variable that is checked when the statement runs. The first condition that is True determines which block executes; if none are True, the else block runs.

 
# Move the robot forward or reverse
# based on the position of the joystick
def when_axis_changed():
    position = controller.axis1.position()
    if position > 0:
        robot.move_at(0)
    elif position < 0:
        robot.move_at(180)
    else:
        robot.stop_all_movement()

controller.axis1.changed(when_axis_changed)

While#

while repeatedly runs code as long as the condition is True. It can also be used like a “forever” by using True as the condition, or a “wait until” by adding not to the condition, as shown in the examples below.

Usage:

while condition:
    pass

Components

Description

condition

An expression or variable that is checked before each iteration. If it is True, the loop continues; if it is False, the loop stops.

 
# Keep the LEDs green while the robot is moving
robot.move_for(200, 0, wait=False)
while robot.is_move_active():
    robot.led.on(ALL_LEDS, GREEN)
    wait(50, MSEC)

robot.led.on(ALL_LEDS, BLACK)


while True:
    # Continually flash all LEDs red then green.
    robot.led.on(ALL_LEDS, RED)
    wait(0.5, SECONDS)
    robot.led.on(ALL_LEDS, GREEN)
    wait(0.5, SECONDS)


# Wait until the screen is pressed before
# turning off the LEDs
while not robot.screen.pressing():
    robot.led.on(ALL_LEDS, RED)
    wait(50, MSEC)

robot.led.on(ALL_LEDS, BLACK)

Break#

break exits a loop immediately. break can be used to leave loops that otherwise would loop forever.

# Flash LEDs until the screen is pressed
while True:
    robot.led.on(ALL_LEDS, RED)
    wait(0.5, SECONDS)
    robot.led.on(ALL_LEDS, GREEN)
    wait(0.5, SECONDS)

    if robot.screen.pressing():
        break

# Turn the LEDs Off
robot.led.off(ALL_LEDS)

Stop Program#

stop_program ends a running project.

Usage:
robot.stop_program()

Parameters

Description

This method has no parameters.

 
# Stop the project once the screen is pressed
while True:
    robot.led.on(ALL_LEDS, RED)
    wait(0.5, SECONDS)
    robot.led.on(ALL_LEDS, GREEN)
    wait(0.5, SECONDS)
    if robot.screen.pressing():
        robot.stop_program()

Pass#

pass is a placeholder for future code and can be used to avoid errors in empty loops, conditionals, and functions.

if condition:
    pass


def function():
    pass
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