6.7. Debugging¶
As you start writing bigger programs, you might find yourself spending more time debugging. More code means more chances to make an error and more places for bugs to hide.
One way to cut your debugging time is “debugging by bisection.” For example, if there are 100 lines in your program and you check them one at a time, it would take 100 steps.
Instead, try to break the problem in half. Look at the middle of the
program, or near it, for an intermediate value you can check. Add a
print statement (or something else that has a verifiable
effect) and run the program.
If the mid-point check is incorrect, the problem must be in the first half of the program. If it is correct, the problem is in the second half.
Every time you perform a check like this, you halve the number of lines you have to search. After six steps (which is much less than 100), you would be down to one or two lines of code, at least in theory.
In practice it is not always clear what the “middle of the program” is and not always possible to check it. It doesn’t make sense to count lines and find the exact midpoint. Instead, think about places in the program where there might be errors and places where it is easy to put a check. Then choose a spot where you think the chances are about the same that the bug is before or after the check.
- writing the entire program at once and looking at the code collectively to find the error
- Incorrect! Debugging the entire program at once is not an example of debugging by bisection. Try again.
- breaking the problem in half and doing "mid-point checks"
- Correct! Debugging by bisection means to split the program in half (or bisections) and debug those separately.
- purposely creating errors in your code to test sections
- Incorrect! Purposefully creating errors is not an example of debugging by bisection (nor is it useful). Try again.
Q-1: An example of “debugging by bisection” is…