197 def env_path(env_var, default, name, checkexists=True):

   198     """get a path specified in a variable or using the default value and return

   199     it.

   200 

   201     :type env_var: str

   202     :param env_var: name of an environment variable

   203 

   204     :type default: str

   205     :param default: default value if the environment variable is not defined

   206 

   207     :type name: str

   208     :param name: the informal name of the path, used for error message

   209 

   210     :rtype: str

   211     :return: the value of the environment variable or the default value

   212 

   213     :raise `ConfigurationError`: if the returned path does not exist

   214     """

   215     path = environ.get(env_var, default)

   216     if checkexists and not exists(path):

   217         raise ConfigurationError('%s directory %s doesn\'t exist' % (name, path))

   218     return abspath(path)

   219 

   220