code: def from_instance_type(cls, instance_type_arg, entrypoint="*"):
          
          if instance_type_arg is None:
              return cls(None)
          if isinstance(instance_type_arg, basestring):
              # By default, all entry points ("*") should use this instance type
              return cls({entrypoint: {"instanceType": instance_type_arg}})
          if isinstance(instance_type_arg, dict):
              # instance_type is a map of entry point to instance type
              return cls({fn: {"instanceType": fn_inst} for fn, fn_inst in instance_type_arg.items()})
          raise DXError('Expected instance_type field to be either a string or a dict')
docs: Returns SystemRequirementsDict that can be passed as a
          "systemRequirements" input to job/new or run/ API calls.
          The instance_type_arg should be either a:
          * string, eg. mem1_ssd1_x2
          * dictionary, eg. {"main": "mem2_hdd2_x2", "other_function": "mem2_hdd2_x1"}