code: def read_dimvalue(self, dimname, path="/", default=NO_DEFAULT):
          
          try:
              dim = self._read_dimensions(dimname, path=path)[0]
              return len(dim)
          except self.Error:
              if default is NO_DEFAULT: raise
              return default
docs: Returns the value of a dimension.
  
          Args:
              dimname: Name of the variable
              path: path to the group.
              default: return `default` if `dimname` is not present and
                  `default` is not `NO_DEFAULT` else raise self.Error.