10.8. Studio: Errors and Debugging¶
The code in this project is broken! Your job is to fix it so we can clear a rocket for launch.
Requirements:
Launch the rocket only if the fuel, crew and computer all check out OK.
If a check fails, print that information to the console and scrub the launch.
If all checks be successful, print a countdown to the console followed by “Liftoff!”
10.8.1. Fix Syntax Errors First¶
Find this code at repl.it.
Run the following code as-is and examine the error message. Fix the mistake, and then re-run the code to check it.
launch_ready = False fuel_level = 17000 if fuel_level >= 20000 print('Fuel level cleared.') launch_ready = True else: print('WARNING: Insufficient fuel!') launch_ready = False
The next block of code hides two syntax errors. Run the code as-is to find the mistakes.
Tip: Only ONE error gets flagged at a time. Fix that ONE problem, and then re-run the code to check your work. Avoid trying to fix multiple issues at once.
launch_ready = False crew_status = True computer_status = 'green' if crew_status and computer_status = 'green': print('Crew & computer cleared.') launch_ready = True else: print('WARNING: Crew or computer not ready!') launch_ready = False if (launch_ready): print("10, 9, 8, 7, 6, 5, 4, 3, 2, 1...") print("Fed parrot...") print("Ignition...") print("Liftoff!') else: print("Launch scrubbed.")
10.8.2. Fix Runtime Errors Next¶
Fix this code at repl.it.
Remember to examine the error message for clues about what went wrong. Pay close attention to any line numbers given in the message—these will help you locate and repair the bug.
launch_ready = False fuel_level = 27000 if fuel_Level >= 20000: print('Fuel level cleared.') launch_ready = True else: print('WARNING: Insufficient fuel!') launch_ready = False
Now find and fix the runtime error in a longer code block.
launch_ready = False fuel_level = 27000 if fuel_level >= 20000: print('Fuel level cleared.') launch_ready = True else: print('WARNING: Insufficient fuel!') launch_ready = False if launch_ready: print("10, 9, 8...") print("Fed parrot...") print("6, 5, 4...") print("Ignition...") printt("3, 2, 1...") print("Liftoff!") else: print("Launch scrubbed.")
10.8.3. Solve Logic Errors Last¶
Logic errors do not generate warning messages or prevent the code from running, but the program still does not work right. (Refer to the Fixing Logic Errors section if you need to review).
Fix this code at repl.it.
First, run this sample code as-is and examine the output. Should the rocket have launched? Did it?
Do not worry about fixing the code yet. You will do that in the next steps.
Let’s break the code down into smaller chunks. Consider the first
if/else
block below.if fuel_level >= 20000: print('Fuel level cleared.') launch_ready = True else: print('WARNING: Insufficient fuel!') launch_ready = False
Comment out lines 14 - 25 in the code editor.
Add
print("launch_ready =", launch_ready)
after the first block, then run the program.Given the
fuel_level
value, shouldlaunch_ready
beTrue
orFalse
after the check? Is the program behaving as expected?
Now consider the second
if/else
block. Add anotherprint("launch_ready =", launch_ready)
after this block and run the program.if crew_status and computer_status == 'green': print('Crew & computer cleared.') launch_ready = True else: print('WARNING: Crew or computer not ready!') launch_ready = False
Given
crew_status
andcomputer_status
, shouldlaunch_ready
beTrue
orFalse
after this check? Is the program behaving as expected?Now consider both
if/else
blocks together (keeping the addedprint
lines). Run the code and examine the output.launch_ready = False fuel_level = 17000 crew_status = True computer_status = 'green' if fuel_level >= 20000: print('Fuel level cleared.') launch_ready = True else: print('WARNING: Insufficient fuel!') launch_ready = False print("launch_ready =", launch_ready) if crew_status and computer_status == 'green': print('Crew & computer cleared.') launch_ready = True else: print('WARNING: Crew or computer not ready!') launch_ready = False print("launch_ready =", launch_ready)
Given the values for
fuel_level
,crew_status
andcomputer_status
, shouldlaunch_ready
beTrue
orFalse
? Is the program behaving as expected?Ah ha! The value of
launch_ready
assigned in the firstif/else
block got changed in the secondif/else
block. This is a common mistake—using the same variable to track the results of two separate conditionals.Since the issue is with
launch_ready
, ONE way to fix the logic error is to use a different variable to store the fuel check result. Make your code do this, then check if your change works by updating the firstprint
statement.Almost done! Modify the final
if/else
block to print the countdown and"Liftoff!"
if both the fuel check andlaunch_ready
variables areTrue
. Print"Launch scrubbed"
if either check fails.