code: def executable(self, step_name, default=None):
      if default is not None:
          return default
      return self._python()
  
imports: import os
  import platform
  import sys
  from .util import get_username
  from .None import metaflow_version
  from metaflow.exception import MetaflowException
  from metaflow.extension_support import dump_module_info
  from metaflow.mflog import BASH_MFLOG
  from .None import R
label_desc: Use image node_id 13 for calling the MetaflowEnvironment obj's underlying member method code with example usage: obj.executable(step_name, default) and returns: self, default