code: def cast(type_name, value, **opts):
      
      type_name, opts = _field_options(type_name, opts)
      return converter(type_name).cast(value, **opts)
docs: Convert a given string to the type indicated by ``type_name``.
  
      If ``None`` is passed in, it will always be returned.
      Optional arguments can include ``true_values`` and ``false_values`` to
      describe boolean types, and ``format`` for dates.