Named Tuples

This script allows you a fast, lightweight attribute-style access to tuples. It contains a function that returns a new subclass of tuple with named fields.

The principal features are:
- Easy to type/read/modify function signature: NamedTuple('Person', 'name age sex height nationality') 
- C-speed attribute lookup using property and itemgetter.
- No instance dictionary means that instances take no more space than a regular tuple. 
- Nice docstring is helpful with an editor's tooltips. 
- Optional keywords in the contructor for readability and to allow variable order of specifying arguments: Person(name='susan', height=60, nationality='english', sex='f', age=30). 
- Key/Value style repr for clearer error messages and for usability at the interactive prompt. 
- Named tuples are picklable.
- Clean error messages for missing or misnamed arguments. 
- A method similar to str.replace() using a field name (used instead of slicing for updating fields -- instead of t[:2] newval t[3:], write t.replace('f',newval)).