Called by the str built-in function.

x.__str__() <==> str(x)

Returns a CF-netCDF-like string of the cell method.

Note that if the intention is to use this string in a CF-netCDF cell_methods attribute then, unless they are standard names, the axes names will need to be modified to be netCDF dimension names.

New in version (cfdm): 1.7.0