Swapped static method call for dict lookup.

This will fail with an honest exception (`KeyError` mentioning the key)
if an invalid value is encountered, rather than an `AttributeError`
claiming `NoneType` has no attribute called `objects` by falling off
the function.

Side effect: 15% faster in `%timeit` tests.
Added brief doctoring pointing at wiki.
Removal of unneeded `__repr__`
Updated text representations for consistency.
Whitespace changes.