[Python] Private underline identifier

1. Python uses underscores as the variable prefix and suffix to specify special variables.

_xxx: No ' from module import * ' is generally considered private and is not available for use outside the module or class.

__XXX__: System-defined Name

__XXX: Private variable name in class

2. Determine if the module is being imported or executed directly

If the module is imported, the value of __name__ is the module name.

If the module is executed directly, the value of __name__ is ' __main__ '

[Python] Private underline identifier