It underlined the special significance python

1. identifiers beginning with a single underscore: indicates not directly accessible (e.g., the _width) class attribute, not by introducing from XXX import *

Private members of the class represented: 2. identifiers beginning with a double underscore (__ add as)

3. The double-underlined are the beginning and end of the python in the specific identity, e.g. __init __ () Constructor represents