For Loops with Ranges in Python

In Python programming, the for i in range loop is a fundamental construct that allows you to iterate over a sequence of numbers, executing a block of code multiple times efficiently. This is similar to the while True loops we have previously explored, but with more control over the number of repetitions and better readability.

Understanding for i in range Loops

In Python, for i in range is commonly used with the range() function, which generates a sequence of numbers. Here’s a basic structure, copy and paste this into your code.py file and observe the output in your serial console:

# Using a 'for' loop with 'range' to repeat an action
for i in range(5):
    print("This is iteration number:", i)

• Loop Definition: for i in range(5): This line defines a loop that will iterate five times. The loop variable i starts at 0 and goes up to 4 (one less than the number provided).
• Repeating Actions: print("This is iteration number:", i) The loop repeats this action, updating the loop variable i each time.

Parameters of range()

The range() function can take different parameters to tailor the sequence of numbers:

1. Single Parameter: range(stop) generates numbers from 0 up to (but not including) stop.
2. Two Parameters: range(start, stop) generates numbers from start to stop (excluding stop).
3. Three Parameters: range(start, stop, step) generates numbers from start to stop, incrementing by step. If step is negative, the numbers will decrement.

Here’s how these parameters can be used:

# Numbers from 0 to 4
for i in range(5):
    print(i)

# Numbers from 2 to 5
for i in range(2, 6):
    print(i)

# Numbers from 10 to 1, decreasing by 2
for i in range(10, 0, -2):
    print(i)

Practice 1

1. Experiment with range() by running this code:

for i in range(1, 10, 2): 
    print("Odd number:", i)

How does changing the parameters modify the output sequence?

Applying for Loops in Robotics

In robotics, loops are essential for repeated actions like moving a robot forward or reading sensor data multiple times.

Using Delays in For Loops:

We can also use time delays in for loops just like in while loops to see the iteration more clearly. This is generally advised for debugging purposes, but not super helpful for when we’re actually running code, unless the time.sleep() value in minimal.

1. Import the time module and use time.sleep() for delays.
2. Write and run the following code:

import time
for i in range(5):
    print("This is in a loop! We're on interation number:", i)
    time.sleep(1)
print("The loop has finished")

Example: Moving a Robot Forward

Assume you have a function move_forward(steps) that moves the robot forward by a given number of steps. You can use for loops to move the robot a specific way:

# Move the robot forward 5 steps, 3 times
for i in range(3):
    move_forward(5)

Challenge 1: Looping for Tasks

Use a for loop to simulate a robot lifting objects repeatedly. Each lift takes one unit of energy, and you want the robot to lift 4 objects.

# Define a function 'lift_object()' that prints "Object lifted". This will be a placeholder statement
def
# Use a 'for' loop to call 'lift_object()' 4 times

Click to reveal a hint

# Create the function with 'def lift_object():' and inside, use 'print("Object lifted")'.
# Use 'for i in range(4):' to call the function multiple times.

Challenge 2: Countdown for Launch

Create a countdown from 10 to 1 before a robot launch using a loop.

# Use a 'for' loop to count down from 10 to 1
for
    # Print each number in the countdown
# Print "Launch!" after the loop

Click to reveal a hint

# Use 'for i in range(10, 0, -1)' for counting down from 10 to 1.
# Ensure you print "Launch!" outside of the loop.

Challenge 3: Adjusting Parameter Values

Your task is to create a loop that modifies the speed of the robot incrementally from 1 to 5 units.

# Assume a function 'set_speed(speed)' sets the robot's speed
def set_speed(speed):
    print("speed", speed, "set!")

# Use a 'for' loop to increase speed from 1 to 5
for
    # Call 'set_speed(speed)' inside the loop

Click to reveal a hint

# Iterate with 'for speed in range(1, 6):' to change the speed from 1 to 5 inclusive.
# Call 'set_speed(speed)' within each iteration of the loop.

As you practice more, you’ll appreciate the power and flexibility these loops provide!