choices.py

from collections import Mapping, namedtuple

def choices(fields):
    '''Create a tuple-like instance appropriate for Django's ``Field.choices``.
    
    Additionally the returned instance also supports attribute access by field name.
    
    Example usage::
    
        >>> t = choices(enumerate(['abc', 'pqr', 'xyz']))
        >>> list(t)
        [(0, 'abc'), (1, 'pqr'), (2, 'xyz')]
        >>> (t.abc, t.pqr, t.xyz)
        (0, 1, 2)
        >>> list(choices({0:'abc', 1:'pqr', 2:'xyz'}))
        [(0, 'abc'), (1, 'pqr'), (2, 'xyz')]
        >>> list(choices(['abc', 'pqr', 'xyz']))
        [('abc', 'abc'), ('pqr', 'pqr'), ('xyz', 'xyz')]
        >>> list(choices('abc pqr xyz'))
        [('abc', 'abc'), ('pqr', 'pqr'), ('xyz', 'xyz')]
        
    :param fields: It can be:
        1. An iterable of ``(value, name)`` tuples.
        2. A ``{value: name}`` mapping.
        3. An iterable of names. Equivalent to an iterable of ``(name, name)``
           tuples, i.e. the names are used as values too.
        4. A space and/or comma separated string. Equivalent to (3) after
           splitting it.
    '''
    clsname = 'Choices_%d' % id(fields)
    if isinstance(fields, basestring):
        cls = namedtuple(clsname, fields)
        values = cls._fields
    elif isinstance(fields, Mapping):
        cls = namedtuple(clsname, fields.itervalues())
        values = fields.keys()
    else:
        values, names = [], []
        for field in fields:
            if isinstance(field, basestring):
                value = name = field
            else:
                value, name = field
            names.append(name)
            values.append(value)
        cls = namedtuple(clsname, names)
    if len(values) != len(set(values)):
        raise ValueError('Field values must be unique')
    items = zip(values, cls._fields)
    cls.__iter__ = lambda self: iter(items)
    return cls(*values)

if __name__ == '__main__':
    import doctest; doctest.testmod()