def __str__(self):
    ' print out some basic information about the BC object '
    string = ('BCs: -x: %s  +x: %s ' % (self.xlb, self.xrb))
    return string
print out some basic information about the BC object
def __str__(self):
    '  '
    string = ('BCs: -x: %s  +x: %s ' % (self.xlb, self.xrb))
    return string