code: def colfieldnames(self, columnname, keyword=''):
          
          if isinstance(keyword, str):
              return self._getfieldnames(columnname, keyword, -1)
          else:
              return self._getfieldnames(columnname, '', keyword)
docs: Get the names of the fields in a column keyword value.
  
          The value of a keyword can be a struct (python dict). This method
          returns the names of the fields in that struct.
          Each field in a struct can be a struct in itself. Names of fields in a
          sub-struct can be obtained by giving a keyword name consisting of
          multiple parts separated by dots (e.g. 'key1.sub1.sub2').
  
          If an empty keyword name is given (which is the default), all keyword
          names of the column are shown and its behaviour is the same as
          :func:`colkeywordnames`.
  
          Instead of a keyword name an index can be given which returns the names
          of the struct value of the i-th keyword.