Convert a string into a Dimension

def from_string(cls, string):
    """Convert a string into a Dimension"""
    # Note: There is some ambiguity as to whether the string passed is intended
    # to become a unit looked up by name or suffix, or a Dimension descriptor.
    if string in units.UNITS_BY_ALL:
      return cls(description=string, unit=units.Unit(string))
    else:
      return cls(description=string)