AFAICT, on Windows using the posix_putenv_garbage dict is unnecessary. The Windows C runtime creates a private copy of the string, so there's no need to keep a reference. Moreover, since there's no unsetenv, deleting a variable is accomplished by calling putenv with an empty value, e.g. putenv('foo', ''). This leaks an item in posix_putenv_garbage, which is left set as ('foo', 'foo=').