underescore_exoplanations_in_Variables

- _single_leading_underscore: weak "internal use" indicator.  E.g. "from M   import *" does not import objects whose name starts with an underscore.- single_trailing_underscore_: used by convention to avoid conflicts with   Python keyword, e.g.    Tkinter.Toplevel(master, class_='ClassName')- __double_leading_underscore: when naming a class attribute, invokes name   mangling (inside class FooBar, __boo becomes _FooBar__boo; see below).- __double_leading_and_trailing_underscore__: "magic" objects or   attributes that live in user-controlled namespaces.  E.g. __init__,   __import__ or __file__.  Never invent such names; only use them   as documented.