code: def url_to_prefix(self, id):
          '''url_to_prefix
  
          High-level api: Convert an identifier from `{namespace}tagname` notation
          to `prefix:tagname` notation. If the identifier does not have a
          namespace, it is assumed that the whole identifier is a tag name.
  
          Parameters
          ----------
  
          id : `str`
              Identifier in `{namespace}tagname` notation.
  
          Returns
          -------
  
          str
              Identifier in `prefix:tagname` notation.
          '''
  
          ret = re.search('^{(.+)}(.+)$', id)
          if ret:
              return self.urls[ret.group(1)] + ':' + ret.group(2)
          else:
              return if url_to_prefix(self, id):
          '''url_to_prefix
  
          High-level api: Convert an identifier from `{namespace}tagname` notation
          to `prefix:tagname` notation. If the identifier does not have a
          namespace, it is assumed that the whole identifier is a tag name.
  
          Parameters
          ----------
  
          id : `str`
              Identifier in `{namespace}tagname` notation.
  
          Returns
          -------
  
          str
              Identifier in `prefix:tagname` notation.
          '''
  
          ret = re.search('^{(.+)}(.+)$', id)
          if ret:
              return self.urls[ret.group(1)] + ':' + ret.group(2)
          else:
              return id
docs: url_to_prefix
  
          High-level api: Convert an identifier from `{namespace}tagname` notation
          to `prefix:tagname` notation. If the identifier does not have a
          namespace, it is assumed that the whole identifier is a tag name.
  
          Parameters
          ----------
  
          id : `str`
              Identifier in `{namespace}tagname` notation.
  
          Returns
          -------
  
          str
              Identifier in `prefix:tagname` notation.