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Quiz: Control Flow, Functions, and Exception Handling

Test your understanding of conditionals, loops, functions, scope, and exception handling with these questions.

1. In an if/elif/else chain, how does Python decide which branch to execute?

  1. It runs every branch that has a True condition
  2. It checks conditions from top to bottom and runs the first branch that is True, then skips the rest
  3. It always runs the else branch last, in addition to whichever branch matched
  4. It evaluates all conditions simultaneously and picks the most specific one
Show Answer

The correct answer is B. Python evaluates conditions in order, from the first if downward. The moment one condition is True, it runs that block and skips all remaining elif and else branches. Exactly one branch runs per execution. This is important for the collision avoidance code: only the most urgent distance condition (closest match first) triggers the robot's response.

Concept Tested: Elif and Else Clauses

2. What is the key difference between a for loop and a while loop?

  1. for loops can only iterate over numbers; while loops can iterate over strings
  2. for loops repeat a fixed number of times or over a sequence; while loops repeat as long as a condition is True
  3. while loops are faster than for loops at the same task
  4. for loops require a break statement to stop; while loops stop automatically
Show Answer

The correct answer is B. A for loop is used when you know in advance how many repetitions you need, or when iterating over every item in a list. A while loop continues as long as its condition is True — ideal for running the robot's main loop forever (with while True:) or waiting until a sensor reads below a threshold. Neither loop type requires break to stop in normal usage.

Concept Tested: For Loop / While Loop

3. What happens when you call stop_motors() in the following code? def stop_motors(): print("Motors stopped.")

  1. An error occurs because stop_motors was never assigned a value
  2. The function definition runs again and redefines the function
  3. The code inside the function runs — it prints "Motors stopped."
  4. Nothing happens because function definitions only run when the program starts
Show Answer

The correct answer is C. Calling a function by writing its name followed by parentheses causes the body of the function to execute at that moment. The def keyword only defines the function — it does not run it. Calling stop_motors() makes the program jump into the function body, run print("Motors stopped."), and then return to where it was called.

Concept Tested: Function Definition

4. What is a local variable in MicroPython?

  1. A variable defined in config.py that only controls the left motor
  2. A variable created inside a function that exists only for the duration of that function call
  3. A variable that stores data on the board's local flash memory, not in RAM
  4. A variable that can be read by any function in the entire program
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The correct answer is B. A local variable is created inside a function and disappears when the function ends. It cannot be accessed from outside the function. This prevents naming conflicts — two different functions can both have a local variable named speed without interfering with each other. Option D describes a global variable, which lives outside all functions.

Concept Tested: Scope and Local Variables

5. Why do robot programs use while True: as the main loop?

  1. It is the only loop type that can call functions
  2. It makes the program use less memory than a for loop
  3. The robot should continuously check sensors and respond to the environment until explicitly stopped
  4. while True is the only valid way to import the time module
Show Answer

The correct answer is C. A robot's job is never "done" in the traditional sense — it should keep sensing and reacting until you decide to stop it. while True creates an infinite loop that runs forever. You stop it deliberately (by pressing Ctrl+C in Thonny), which the program handles using a try/except KeyboardInterrupt block. It has no relationship to function calls or imports.

Concept Tested: While Loop

6. What is the purpose of the finally block in a try/except/finally structure?

  1. It catches errors that the except block missed
  2. It runs only when no exception occurred — it is the success path
  3. It runs no matter what — even if an exception occurred or Ctrl+C was pressed — so cleanup always executes
  4. It restarts the try block from the beginning after an exception is handled
Show Answer

The correct answer is C. The finally block is guaranteed to run regardless of whether the try block succeeded, an exception was caught by except, or the program was stopped with Ctrl+C (KeyboardInterrupt). This makes it the correct place for hardware cleanup code — stopping motors, turning off LEDs — so the robot always shuts down safely even after a crash.

Concept Tested: Try Except Finally

7. When a function modifies a global variable, what keyword must be used inside the function?

  1. extern
  2. global
  3. shared
  4. public
Show Answer

The correct answer is B. To modify a global variable from inside a function, you must declare it with the global keyword at the start of the function: global is_moving. Without this, Python creates a new local variable with the same name inside the function, leaving the global unchanged. The keywords extern, shared, and public do not exist in Python — they come from other languages.

Concept Tested: Global Variables

8. What does from time import sleep do differently from import time?

  1. from time import sleep is faster because it skips loading the rest of the time module
  2. from time import sleep allows you to call sleep(1) directly; import time requires time.sleep(1)
  3. from time import sleep makes sleep() available only inside functions, not at the top level
  4. from time import sleep imports an older, slower version of the sleep function
Show Answer

The correct answer is B. When you write from time import sleep, you import just the sleep name into your local namespace. You can then call it as sleep(1). With import time, the module is loaded under the name time, and you must call time.sleep(1). Both access the same function — the difference is how you reference it. The from...import style is more concise for frequently used functions.

Concept Tested: Importing Modules

9. How does ticks_diff() differ from simply subtracting two ticks_ms() values?

  1. ticks_diff() measures time in microseconds while subtraction measures milliseconds
  2. ticks_diff() handles the counter wrapping around (overflow) correctly; plain subtraction fails after about 12 days of uptime
  3. ticks_diff() pauses the program while waiting; subtraction returns immediately
  4. ticks_diff() only works inside interrupt handlers; subtraction works everywhere
Show Answer

The correct answer is B. The ticks_ms() counter has a maximum value and wraps back to zero (overflows) after a period of time. When this happens, plain subtraction gives a negative or incorrect result. ticks_diff(newer, older) is designed to handle this overflow correctly, always returning the right elapsed time. For a robot that might run for hours, using ticks_diff is the safe choice.

Concept Tested: Timers and Delays

10. What is the correct way to write a function that returns the larger of two numbers?

  1. def bigger(a, b): print(a if a > b else b)
  2. def bigger(a, b): return a if a > b else b
  3. def bigger(a, b): bigger = a if a > b else b
  4. bigger(a, b) = a if a > b else b
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The correct answer is B. The return keyword sends a value back to the caller. Using print() (A) only displays the result — the caller cannot use the value in further calculations. Option C stores the result in a local variable but never sends it back. Option D is not valid Python syntax — function definitions require the def keyword and the body must be indented.

Concept Tested: Return Values