code: def add_part(self, part):
          
          if isinstance(part, RE_TYPE):
              part = part.pattern
  
          # Allow U / spmething syntax
          if self == '^$':
              return URLPattern(part, self.separator)
          else:
              # Erase dup separator inbetween
              sep = self.separator
              return URLPattern(self.rstrip('$' + sep) + sep + part.lstrip(sep),
                                sep)
docs: Function for adding partial pattern to the value
          :param part: string or compiled pattern