code: def select_scheme(self, name):
          
          # it's the caller's problem if they supply a bad name!
          scheme = INSTALL_SCHEMES[name]
          for key in SCHEME_KEYS:
              attrname = 'install_' + key
              if getattr(self, attrname) is None:
                  setattr(self, attrname, scheme[key])
docs: Sets the install directories by applying the install schemes.