kindergarten-garden: improve example.py (#1843)
kindergarten-garden: improve example.py (#1843)

* kindergarten-garden: improve example

Eliminate mutable default value and incorrect use of name mangling.
Minimize unused instance attributes and speed up performance.

* kindergarten-garden: improve example

Eliminate mutable default value and incorrect use of name mangling.
Minimize unused instance attributes and speed up performance.

* kindergarten-garden: line length fix

behrtam/xpython,exercism/xpython,jmluy/xpython,smalley/python,exercism/xpython,jmluy/xpython,behrtam/xpython,exercism/python,exercism/python,smalley/python