控制

介绍

Control includes methods for timing, program flow, conditional logic, and project termination. These controls let you pause execution, create loops, define logic paths, and end a project.

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

• wait – Pauses execution for a given number of milliseconds or seconds.

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

• if – Executes 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)

参数	描述
time	等待的时间量，以正整数表示。
units	The unit to represent the time: MSEC (default) — milliseconds SECONDS

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

For

for iterates over a sequence (such as a list, tuple, dictionary, set, or string) or any iterable object. It executes the block of code once for each item in the sequence.

使用量：

for value in expression_list:
    pass

Components	描述
value	存储迭代中的当前元素的临时变量。
expression_list	循环遍历的元素集合（例如，列表、字符串、范围）。

# 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()

If

if executes the indented block of code if the condition evaluates to True.

用法：

if condition:
    pass

参数	描述
condition	An expression or variable that is evaluated when the statement runs. If it evaluates to True, the code inside the if block executes; if it evaluates to 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 evaluates to True or False.

用法：

if condition:
    pass
else:
    pass

参数	描述
condition	An expression or variable that is evaluated when the statement runs. If it evaluates to True, the code inside the if block executes; if it evaluates to 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 evaluates to True.

• elif checks additional conditions only if all previous conditions evaluated t0 False. Multiple elif statements can be used.

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

用法：

if condition:
    pass
elif condition:
    pass
else:
    pass

参数	描述
condition	An expression or variable that is evaluated when the statement runs. The first condition that evaluates to 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 “Wait until” by adding not to the condition, as shown in the example below.

用法：

while condition:
    pass

参数	描述
condition	An expression or variable that is evaluated before each iteration. If it evaluates to True, the loop continues; if it evaluates to 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.

使用量：

break

参数	描述
	This keyword has no parameters.

# 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()

参数	描述
	该方法没有参数。

# 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