code: def get(self, option, default=undefined, cast=undefined):
          
  
          # We can't avoid __contains__ because value may be empty.
          if option in os.environ:
              value = os.environ[option]
          elif option in self.repository:
              value = self.repository[option]
          else:
              if isinstance(default, Undefined):
                  raise UndefinedValueError('{} not found. Declare it as envvar or define a default value.'.format(option))
  
              value = default
  
          if isinstance(cast, Undefined):
              cast = self._cast_do_nothing
          elif cast is bool:
              cast = self._cast_boolean
  
          return cast(value)
docs: Return the value for option or default if defined.