CodeSOD: Ready Xor Not

Phil's company hired a contractor. It was the typical overseas arrangement: bundle up a pile of work, send it off to another timezone, receive back terrible code, push back during code review, then the whole thing blows up when the contracting company pushes back about how while the code review is in the contract if you're going to be such sticklers about it, they'll never deliver, and then management steps in and says, "Just keep the code review to style comments," and then it ends up not mattering anyway because the contractor assigned to the contract leaves for another contracting company, and management opts to use the remaining billable hours for a new feature instead of finishing the inflight work, so you inherit a half-finished pile of trash and somehow have to make it work.

Like I said, pretty standard stuff.

Phil found this construct scattered all over the codebase:

if cond1 and cond2:
	pass
elif cond1 or cond2:
	# do actual work

I hesitate to post this, because what we're looking at is just an attempt at doing a xor operation. And it's not wrong– it's an if statement way of writing (not a and b) or (a and not b). And if we're being nit-picky, while Python has a xor operator, it's technically a bitwise xor, so I could see someone not connecting that they could use it in this case- cond1 ^ cond2 would work just fine, so long as both conditions are actual booleans. But Python often uses non-boolean comparisons, like:

text = ""
if text:
  print("This won't print.")

This is playing with truthiness, and the problem here is that you can't use a xor to chain these conditions together.

if text ^ otherText:
	# do stuff

That's a runtime error, as the ^ is only defined for integral types. You'd have to write:

if bool(text) ^ bool(otherText):
	# do stuff

So, would it have been better to use one of the logical equivalences for xor? Certainly. Would it have been even better to turn that equivalence into a function so you could actually call a xor function? Absolutely.

But I also can't complain too much about this one. I hate it, don't get me wrong, but it's not a trainwreck.

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