154 lines
5.1 KiB
Python
154 lines
5.1 KiB
Python
from __future__ import unicode_literals
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import copy
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class Choices(object):
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"""
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A class to encapsulate handy functionality for lists of choices
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for a Django model field.
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Each argument to ``Choices`` is a choice, represented as either a
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string, a two-tuple, or a three-tuple.
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If a single string is provided, that string is used as the
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database representation of the choice as well as the
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human-readable presentation.
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If a two-tuple is provided, the first item is used as the database
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representation and the second the human-readable presentation.
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If a triple is provided, the first item is the database
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representation, the second a valid Python identifier that can be
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used as a readable label in code, and the third the human-readable
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presentation. This is most useful when the database representation
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must sacrifice readability for some reason: to achieve a specific
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ordering, to use an integer rather than a character field, etc.
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Regardless of what representation of each choice is originally
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given, when iterated over or indexed into, a ``Choices`` object
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behaves as the standard Django choices list of two-tuples.
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If the triple form is used, the Python identifier names can be
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accessed as attributes on the ``Choices`` object, returning the
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database representation. (If the single or two-tuple forms are
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used and the database representation happens to be a valid Python
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identifier, the database representation itself is available as an
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attribute on the ``Choices`` object, returning itself.)
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Option groups can also be used with ``Choices``; in that case each
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argument is a tuple consisting of the option group name and a list
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of options, where each option in the list is either a string, a
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two-tuple, or a triple as outlined above.
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"""
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def __init__(self, *choices):
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# list of choices expanded to triples - can include optgroups
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self._triples = []
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# list of choices as (db, human-readable) - can include optgroups
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self._doubles = []
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# dictionary mapping db representation to human-readable
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self._display_map = {}
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# dictionary mapping Python identifier to db representation
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self._identifier_map = {}
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# set of db representations
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self._db_values = set()
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self._process(choices)
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def _store(self, triple, triple_collector, double_collector):
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self._identifier_map[triple[1]] = triple[0]
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self._display_map[triple[0]] = triple[2]
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self._db_values.add(triple[0])
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triple_collector.append(triple)
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double_collector.append((triple[0], triple[2]))
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def _process(self, choices, triple_collector=None, double_collector=None):
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if triple_collector is None:
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triple_collector = self._triples
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if double_collector is None:
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double_collector = self._doubles
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store = lambda c: self._store(c, triple_collector, double_collector)
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for choice in choices:
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if isinstance(choice, (list, tuple)):
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if len(choice) == 3:
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store(choice)
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elif len(choice) == 2:
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if isinstance(choice[1], (list, tuple)):
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# option group
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group_name = choice[0]
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subchoices = choice[1]
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tc = []
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triple_collector.append((group_name, tc))
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dc = []
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double_collector.append((group_name, dc))
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self._process(subchoices, tc, dc)
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else:
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store((choice[0], choice[0], choice[1]))
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else:
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raise ValueError(
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"Choices can't take a list of length %s, only 2 or 3"
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% len(choice)
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)
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else:
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store((choice, choice, choice))
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def __len__(self):
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return len(self._doubles)
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def __iter__(self):
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return iter(self._doubles)
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def __getattr__(self, attname):
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try:
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return self._identifier_map[attname]
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except KeyError:
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raise AttributeError(attname)
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def __getitem__(self, key):
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return self._display_map[key]
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def __add__(self, other):
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if isinstance(other, self.__class__):
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other = other._triples
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else:
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other = list(other)
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return Choices(*(self._triples + other))
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def __radd__(self, other):
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# radd is never called for matching types, so we don't check here
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other = list(other)
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return Choices(*(other + self._triples))
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def __eq__(self, other):
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if isinstance(other, self.__class__):
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return self._triples == other._triples
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return False
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def __repr__(self):
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return '%s(%s)' % (
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self.__class__.__name__,
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', '.join(("%s" % repr(i) for i in self._triples))
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)
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def __contains__(self, item):
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return item in self._db_values
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def __deepcopy__(self, memo):
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return self.__class__(*copy.deepcopy(self._triples, memo))
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