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enable usage of cache in iterator #35232

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enable usage of cache in iterator #35232

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353e3f6
enable usage of cache in iterator
mantepse Mar 5, 2023
357edbc
add a blank line for the linter
mantepse Mar 5, 2023
caead99
Merge branch 'sagemath:develop' into caching_finite_enumerated_sets
mantepse Mar 1, 2024
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44 changes: 29 additions & 15 deletions src/sage/categories/finite_enumerated_sets.py
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Original file line number Diff line number Diff line change
Expand Up @@ -257,15 +257,14 @@ def _list_from_iterator(self):

.. WARNING::

The overriding of ``self.__iter__`` to use the cache
is ignored upon calls such as ``for x in C:`` or
``list(C)`` (which essentially ruins its purpose).
Indeed, Python looks up the ``__iter__`` method
directly in the class of ``C``, bypassing ``C``'s
dictionary (see the Python reference manual,
`Special method lookup for new-style classes <http://docs.python.org/reference/datamodel.html#special-method-lookup-for-new-style-classes>`_)
It is not enough to assign ``self.__iter__`` to a new
method, we have to override the class. Indeed,
Python looks up the ``__iter__`` method directly in
the class of ``C``, bypassing ``C``'s dictionary (see
the Python reference manual,
`<https://docs.python.org/3/reference/datamodel.html#special-lookup>`_)

Let's take an example::
Let's take an example, illustrating that we do the right thing::

sage: class Example(Parent):
....: def __init__(self):
Expand All @@ -276,11 +275,11 @@ def _list_from_iterator(self):
sage: C = Example()
sage: list(C)
hello!
...
hello!
[1, 2, 3]
sage: list(C)
hello!
...
hello!
[1, 2, 3]

Note that ``hello!`` actually gets printed more than once in
Expand All @@ -294,11 +293,10 @@ def _list_from_iterator(self):
sage: C.list()
[1, 2, 3]

Now we would want the original iterator of ``C`` not
to be called anymore, but that's not the case::
Now the original iterator of ``C`` is also not called
anymore::

sage: list(C)
hello!
[1, 2, 3]

TESTS:
Expand All @@ -316,6 +314,13 @@ def _list_from_iterator(self):
<bound method EnumeratedSets.ParentMethods._unrank_from_iterator of FreshExample>
sage: C.cardinality
<bound method FiniteEnumeratedSets.ParentMethods._cardinality_from_iterator of FreshExample>
sage: C.__iter__
<bound method Example.__iter__ of FreshExample>
sage: C.__class__
<class '__main__.FreshExample_with_category'>

We now trigger the caching::

sage: l1 = C.list(); l1
[1, 2, 3]
sage: C.list
Expand All @@ -325,7 +330,9 @@ def _list_from_iterator(self):
sage: C.cardinality
<bound method FiniteEnumeratedSets.ParentMethods._cardinality_from_list of FreshExample>
sage: C.__iter__
<bound method EnumeratedSets.ParentMethods._iterator_from_list of FreshExample>
<bound method FiniteEnumeratedSets.ParentMethods._list_from_iterator.<locals>.CachedIter.__iter__ of FreshExample>
sage: C.__class__
<class 'sage.categories.finite_enumerated_sets.FreshExample_with_category'>

We finally check that nothing breaks before and after
calling explicitly the method ``.list()``::
Expand All @@ -337,6 +344,7 @@ def _list_from_iterator(self):
sage: C.list()
[1, 2, 3]
sage: TestSuite(C).run()

"""
try:
if self._list is not None:
Expand All @@ -346,10 +354,16 @@ def _list_from_iterator(self):
result = tuple(self.__iter__())
try:
self._list = result
self.__iter__ = self._iterator_from_list
self.cardinality = self._cardinality_from_list
self.tuple = self._tuple_from_list
self.unrank = self._unrank_from_list
name = self.__class__.__name__

class CachedIter(self.__class__):
def __iter__(self):
yield from self._list
self.__class__ = CachedIter
self.__class__.__qualname__ = name
except AttributeError:
pass
return list(result)
Expand Down