Joshua: does your script use os.fork(), or multiprocessing? 

In that case this is a known issue made worse on High Sierra: _scproxy uses Cocoa libraries, and those cause problems when using for without exec. In High Sierra the Cocoa libraries are more strict and are hence more likely to cause problems like this.

There's not much we can do about that, other than avoiding using _scproxy. If you don't use a proxy server setting "no_proxy" in your shell environment should do the trick.