Git bisect exercise

Motivation

The motivation for this exercise is to be able to do archaeology with Git on a source code where the bug is difficult to see visually. Finding the offending commit is often more than half the debugging.

Background

The script get_pi.py approximates pi using terms of the Nilakantha series. It should produce 3.14 but it does not. The script broke at some point and produces 3.57 using the last commit:

$ python get_pi.py

3.57

At some point within the 500 first commits, an error was introduced. The only thing we know is that the first commit worked correctly.

Your task

Clone or fork this repository and use git bisect to find the commit which broke the computation.

How to find the first commit

$ git log --oneline | tail -n 1

Bonus exercise

Write a script that checks for a correct result and use git bisect run to find the offending commit automatically.

Solutions (spoiler alert!)

The offending commit is commit number 137.

And here is a Python script which can be used together with git bisect run to find the offending commit automatically:

import subprocess
import math
import sys

output = subprocess.check_output(['python', 'get_pi.py'])
result = float(output)

if math.isclose(result, 3.14):
    sys.exit(0)
else:
    sys.exit(1)

But you can also try to solve this using a shell script or a script in your favourite language.