vector.txt
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Extending Python 

 Python is a *programmable* programming language

 Python itself is built from classes and objects

 Extend the language seamlessly by definining new classes with special methods

 type means class, including the built-in types like list and int
  note constructor syntax: instead of [] or {}, can use list() or dict()

 object means instance (of a class)
  including even 2, try dir(2), sys.getsizeof(2)

 operator means  special method
  2 + 2  means int('2').__add__(int('2'))
  Dozens of special methods, including index and slicing for data structures

 'class' is just another type, you could define your own: javaclass or ...
  This is called a metaobject protocol




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Add a new type: vector

 vector.py: inspired by numpy array and matrix types

 (Demo: explain vectors - built in list + does the wrong thing, * crashes)

 vector inherits from list - yes, we can inherit from built-in types!

 Special methods: __repr__ redefines print etc, __add__, __mul__ redefine +, *