A combination of broken escaping in CMake and in the python swig generation scripts meant that the swig generation step would fail whenever there were spaces or special characters in parameters passed to swig.
The fix for this in CMakeLists is to use the VERBATIM option on all COMMAND-based custom builders relying on CMake to properly escape each argument in the generated file.
Within the python swig scripts, the fix is to call subprocess.Popen with a list of raw argument strings rather than ones that are incorrectly manually escaped, then passed to a shell subprocess via subprocess.Popen(' '.join(params)). This also prevents nasty things happening such as accidental command-injection.
This allows us to have the swig / python executables in paths containing special chars and spaces, (or on shared storage on Win32, e.g \\some\path or C:\Program Files\swig\swig.exe).