code: def get_args(get_item):
      
      if not isinstance(get_item, dict):
          raise ContextError('envGet must contain a list of dicts.')
  
      env = get_item.get('env', None)
  
      if not env:
          raise KeyNotInContextError(
              'context envGet[env] must exist in context for envGet.')
  
      key = get_item.get('key', None)
  
      if not key:
          raise KeyNotInContextError(
              'context envGet[key] must exist in context for envGet.')
  
      if 'default' in get_item:
          has_default = True
          default = get_item['default']
      else:
          has_default = False
          default = None
  
      return (env, key, has_default, default)
docs: Parse env, key, default out of input dict.
  
      Args:
          get_item: dict. contains keys env/key/default
  
      Returns:
          (env, key, has_default, default) tuple, where
              env: str. env var name.
              key: str. save env value to this context key.
              has_default: bool. True if default specified.
              default: the value of default, if specified.
  
      Raises:
          ContextError: envGet is not a list of dicts.
          KeyNotInContextError: If env or key not found in get_config.