mirror of https://github.com/jab/bidict.git
96 lines
3.5 KiB
PHP
96 lines
3.5 KiB
PHP
.. _sortedbidicts:
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Sorted Bidict Recipes
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#####################
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Suppose you need a bidict that maintains its items in sorted order.
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The Python standard library does not include any sorted dict types,
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but the excellent
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`sortedcontainers <http://www.grantjenks.com/docs/sortedcontainers/>`_ and
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`sortedcollections <http://www.grantjenks.com/docs/sortedcollections/>`_
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libraries do.
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Armed with these along with bidict's
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:attr:`fwd_cls <bidict.BidictBase.fwd_cls>`
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and
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:attr:`inv_cls <bidict.BidictBase.inv_cls>`
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attributes,
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creating a sorted bidict type is dead simple::
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>>> import bidict, sortedcontainers
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>>> # a sorted bidict whose forward items stay sorted by their keys,
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>>> # and whose inverse items stay sorted by *their* keys (i.e. it and
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>>> # its inverse iterate over their items in different orders):
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>>> class SortedBidict1(bidict.bidict):
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... fwd_cls = sortedcontainers.SortedDict
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... inv_cls = sortedcontainers.SortedDict
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... __reversed__ = lambda self: reversed(self.fwdm)
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>>> b = SortedBidict1({'Tokyo': 'Japan', 'Cairo': 'Egypt'})
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>>> b
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SortedBidict1([('Cairo', 'Egypt'), ('Tokyo', 'Japan')])
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>>> b['Lima'] = 'Peru'
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>>> # b stays sorted by its keys:
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>>> list(b.items())
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[('Cairo', 'Egypt'), ('Lima', 'Peru'), ('Tokyo', 'Japan')]
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>>> # b.inv stays sorted by *its* keys (b's values!)
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>>> list(b.inv.items())
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[('Egypt', 'Cairo'), ('Japan', 'Tokyo'), ('Peru', 'Lima')]
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>>> # a sorted bidict whose forward items stay sorted by their keys,
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>>> # and whose inverse items stay sorted by their values (i.e. it and
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>>> # its inverse iterate over their items in the same order):
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>>> import sortedcollections
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>>> class SortedBidict2(bidict.bidict):
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... fwd_cls = sortedcontainers.SortedDict
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... inv_cls = sortedcollections.ValueSortedDict
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... __reversed__ = lambda self: reversed(self.fwdm)
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>>> element_by_atomic_number = SortedBidict2({
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... 3: 'lithium', 1: 'hydrogen', 2: 'helium'})
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>>> # stays sorted by key:
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>>> element_by_atomic_number
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SortedBidict2([(1, 'hydrogen'), (2, 'helium'), (3, 'lithium')])
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>>> # .inv stays sorted by value:
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>>> list(element_by_atomic_number.inv.items())
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[('hydrogen', 1), ('helium', 2), ('lithium', 3)]
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>>> element_by_atomic_number[4] = 'beryllium'
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>>> list(element_by_atomic_number.inv.items())
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[('hydrogen', 1), ('helium', 2), ('lithium', 3), ('beryllium', 4)]
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>>> # order is preserved correctly when passing .inv back into constructor:
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>>> atomic_number_by_element = SortedBidict2(element_by_atomic_number.inv)
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>>> list(atomic_number_by_element.items()) == list(element_by_atomic_number.inv.items())
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True
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>>> # copies of .inv preserve order correctly too:
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>>> list(element_by_atomic_number.inv.copy().items()) == list(atomic_number_by_element.items())
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True
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>>> # To pass method calls through to the _fwd SortedDict when not present
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>>> # on the bidict instance, provide a custom __getattribute__ method:
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>>> def __getattribute__(self, name):
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... try:
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... return object.__getattribute__(self, name)
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... except AttributeError as e:
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... try:
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... return getattr(self.fwdm, name)
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... except AttributeError:
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... raise e
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>>> SortedBidict2.__getattribute__ = __getattribute__
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>>> # bidict has no .peekitem attr, so the call is passed through to _fwd:
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>>> element_by_atomic_number.peekitem()
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(4, 'beryllium')
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