Ah, I see what you mean. In this case, we could change how the case-insensitivity is handled here, but it would only be applicable to 3.7. I'm not opposed to changing the default behavior here, but it does kind of bring up the mapping dict discussion again.

If case is important to your application, environment variables are probably the wrong way to go about passing them in anyway. Either use the value of the variable rather than the key, or find a different approach. Given 'nt.environ' is available without case remapping, I think that's the best workaround.