Opened 5 years ago
Last modified 4 years ago
#24551 closed defect
py3: defining __eq__ breaks inheritance of __hash__ — at Version 36
Reported by:  Frédéric Chapoton  Owned by:  

Priority:  major  Milestone:  sage8.5 
Component:  python3  Keywords:  
Cc:  Jeroen Demeyer, Travis Scrimshaw, François Bissey, Erik Bray, vklein, zerline  Merged in:  
Authors:  Reviewers:  
Report Upstream:  N/A  Work issues:  
Branch:  Commit:  
Dependencies:  Stopgaps: 
Description (last modified by )
This is potentially a largescale problem, as can be seen using
grep L "def __hash__" $(git grep l "def __eq__" )
TODO LIST (extracted from errors on sage/python3 testsuite):
Ticket  Module  Notes 

#25935  AbelianGroupWithValues_class_with_category  group 
#25935  AbelianGroup_class_with_category  group 
#?????  AlternatingGroup_with_category  group 
#26058  BruhatTitsHarmonicCocycles_with_category  
#?????  CartesianProduct_with_category.element_class  
#25940  ChainComplex_class_with_category  
#?????  ClassGroup_with_category  group 
#?????  CompositeConstructionFunctor?  
#26061  CrystalOfAlcovePaths_with_category.element_class  
#26087  CycleIndexSeriesRing_class_with_category  
#?????  CyclicPermutationGroup_with_category  group 
#?????  DiCyclicGroup_with_category  group 
#?????  DihedralGroup_with_category  group 
#26088  EisensteinExtensionFieldCappedRelative_with_category  
#26088  EisensteinExtensionRingCappedAbsolute_with_category  
#26088  EisensteinExtensionRingCappedRelative_with_category  
#26088  EisensteinExtensionRingFixedMod_with_category  
#?????  FiniteWord_list  
#?????  FiniteWord_str  
#?????  FiniteWord_tuple  
#?????  Gamma0_class_with_category  group 
#?????  Gamma1_class_with_category  group 
#?????  GammaH_class_with_category  group 
#?????  Gamma_class_with_category  group 
#26063  HammingCode_with_category  
#25946  HyperellipticCurve_g2_padic_field_with_category  
#25946  HyperellipticCurve_g2_rational_field_with_category  
#25946  HyperellipticCurve_padic_field_with_category  
#25946  HyperellipticCurve_rational_field_with_category  
#?????  IdealMonoid_c_with_category  
#?????  InfinitePolynomialFunctor?  
#?????  KleinFourGroup_with_category  group 
#?????  LabelledBinaryTrees_with_category.element_class  
#?????  MPolynomial_polydict  
#?????  MathieuGroup_with_category  group 
#?????  ModularSymbolsAmbient_wtk_eps_with_category  
#?????  MultivariateProduct_with_category.element_class  
#?????  NCPolynomialIdeal  
#?????  PGL_with_category  group 
#?????  PSL_with_category  group 
#?????  Partitions_with_constraints_with_category  
#?????  PolynomialQuotientRing_domain_with_category  
#?????  PolynomialQuotientRing_field_with_category  
#?????  PolynomialQuotientRing_generic_with_category  
#?????  PrimitiveGroup_with_category  group 
#26091  ProjectiveSpace_rational_field_with_category  
#26091  ProjectiveSpace_ring_with_category  
#?????  QuaternionFractionalIdeal_rational  
#?????  QuaternionGroup_with_category  group 
#?????  SL2Z_class_with_category  group 
#26062  ShiftedPrimedTableaux_shape_with_category.element_class  
#?????  SimplicialSetMorphism?  
#26089  SmoothCharacterGroupQp_with_category  group 
#26089  SmoothCharacterGroupRamifiedQuadratic_with_category  group 
#26089  SmoothCharacterGroupUnramifiedQuadratic_with_category  group 
#26092  SubsetsSorted_with_category  
#26092  Subsets_sk_with_category  
#26064  SymbolicConstantsSubring_with_category  
#?????  SymmetricGroup_with_category  group 
#?????  TransitiveGroup_with_category  group 
#?????  UnivariateProduct_with_category.element_class  
#26088  UnramifiedExtensionFieldCappedRelative_with_category  
#26088  UnramifiedExtensionRingCappedAbsolute_with_category  
#26088  UnramifiedExtensionRingCappedRelative_with_category  
#26088  UnramifiedExtensionRingFixedMod_with_category  
#26058  pAdicAutomorphicForms_with_category  
#?????  sage.rings.padics.qadic_flint_CR.qAdicCappedRelativeElement 
Change History (36)
comment:1 Changed 5 years ago by
comment:2 Changed 5 years ago by
Component:  PLEASE CHANGE → python3 

Type:  PLEASE CHANGE → defect 
I've also, at least, provisionally, implemented __hash__
's for a lot of classes. I haven't pushed any of those changes yet because I've been lazy about adding docstrings for them and need to do that.
There are also lots of cases where it's fine to just assign __hash__ = BaseClass.__hash__
(in fact this is the case for all classes). That said, the default __hash__
a lot of classes have is not very good, or sometimes problematic (e.g. I think some object are hashable even though they're not immutable). So it's a good opportunity to check those on a case base case basis.
comment:3 Changed 5 years ago by
ok. But anyway, this seems to require a lot of work..
I did a few simple cases in #24552
comment:4 Changed 5 years ago by
Of the commits in my python 3 branch that I haven't made tickets for yet, I've added __hash__
implementations in at least the following (and maybe more):
src/sage/algebras/free_algebra.py src/sage/algebras/free_algebra_quotient.py src/sage/algebras/quatalg/quaternion_algebra.py src/sage/algebras/steenrod/steenrod_algebra.py src/sage/categories/pushout.py src/sage/coding/hamming_code.py src/sage/coding/linear_code.py src/sage/combinat/crystals/generalized_young_walls.py src/sage/combinat/integer_vector.py src/sage/combinat/rigged_configurations/rigged_partition.py src/sage/combinat/root_system/type_dual.py src/sage/combinat/species/series.py src/sage/combinat/subset.py src/sage/combinat/subword_complex.py src/sage/combinat/words/word_datatypes.pyx src/sage/groups/abelian_gps/abelian_group.py src/sage/groups/perm_gps/permgroup_named.py src/sage/homology/chain_complex.py src/sage/homology/chain_complex_morphism.py src/sage/manifolds/continuous_map.py src/sage/modular/arithgroup/congroup_generic.py src/sage/modular/modsym/ambient.py src/sage/monoids/free_monoid.py src/sage/rings/fraction_field.py src/sage/rings/ideal_monoid.py src/sage/rings/number_field/order.py src/sage/rings/padics/padic_extension_generic.py src/sage/rings/polynomial/laurent_polynomial_ring.py src/sage/rings/polynomial/polynomial_quotient_ring.py src/sage/structure/element_wrapper.pyx
comment:5 Changed 5 years ago by
src/sage/combinat/rigged_configurations/bij_abstract_class.py
and its subclasses should never be used in a hash (it is a helper class to perform a bijection) and the __eq__
is just there so the TestSuite
with the pickling passes. Probably the better thing to do here is to remove the __eq__
and skip the pickling test (this is some of the first code I contributed to Sage, memories...).
comment:6 Changed 5 years ago by
Quick question one of you can maybe answer: If a class inherits from UniqueRepresentation
, then should it even be implementing __eq__
? ISTM it should just use the __eq__
implementation inherited from UniqueRepresentation
(via WithEqualityById
).
I've found several classes that inherit from UniqueRepresentation
but that still implement their own __eq__
like:
def __eq__(self, other): return isinstance(other, type(self)) and self.foo == other.foo and self.bar == other.bar
for some list of various attributes of the objects that are mostly determined at the object's construction.
I admit I don't fully understand yet how UniqueRepresentation
is supposed to work though (I will read the docs for it carefully now). But it seems like it should implicitly cover this use case (and thus eliminate the need for a lot of explicit __eq__
and hence __hash__
implementations).
comment:7 Changed 5 years ago by
Or could it be that in some of these cases their __eq__
is defined more broadly than just equality by identity? I admit in some of these cases I don't know the mathematical background well enough to determine this, and the given examples don't always make the intent clear either.
comment:8 followup: 9 Changed 5 years ago by
Okay, quoting the docs:
Instances of a class have a unique instance behavior when instances of this class evaluate equal if and only if they are identical.
So IIUC, a class really shouldn't be inheriting UniqueRepresentation
unless they truly do define equality by identity. So either these classes shouldn't be defining __eq__
, or they aren't using UniqueRepresentation
appropriately (and should perhaps just be using CachedRepresentation
at the most).
comment:9 Changed 5 years ago by
Replying to embray:
So IIUC, a class really shouldn't be inheriting
UniqueRepresentation
unless they truly do define equality by identity. So either these classes shouldn't be defining__eq__
, or they aren't usingUniqueRepresentation
appropriately (and should perhaps just be usingCachedRepresentation
at the most).
That sounds reasonable.
comment:10 Changed 5 years ago by
I'm just going through sage.algebras
and finding several cases like this (this is where I started since that's where I was recently toiling on the __hash__
issue). Indeed, it seems many of these classes predate, and/or have __eq__
methods that predate UniqueRepresentation
.
comment:11 Changed 5 years ago by
Another angle to this that Jeroen has already pointed out a couple times is that there is InheritComparison
. This could be extended to also automatically force the inheritance of __hash__
. I think that would solve a lot of this "for free". But what I've also found is that this has exposed many cases where class's default inherited __hash__
es are not welldefined w.r.t. their __eq__
, or other issues like in #25387.
In other words, I think that the new behavior in Python 3, while annoying in terms of how much it breaks in Sage, is good that it forces us to think more carefully about this. So I'd be hesitant to resort to such a bruteforce fix except as a last resort.
comment:12 Changed 4 years ago by
Among the files listed in the ticket description, the case
src/sage/manifolds/continuous_map.py
is dealt with by #25502. The other manifold cases:
src/sage/manifolds/chart.py src/sage/manifolds/chart_func.py src/sage/manifolds/differentiable/affine_connection.py src/sage/manifolds/differentiable/tensorfield.py src/sage/manifolds/scalarfield.py
should trigger no Python3 issue since none of these classes is intended to be hashable. Same thing for
src/sage/tensor/modules/comp.py src/sage/tensor/modules/free_module_morphism.py src/sage/tensor/modules/free_module_tensor.py src/sage/tensor/modules/tensor_with_indices.py
comment:14 Changed 4 years ago by
some failures in sage3 doctests:
'TypeError("unhashable type: \'AbsoluteOrder_with_category\'",)', 'TypeError("unhashable type: \'RelativeOrder_with_category\'",)', "TypeError: unhashable type: 'AbelianGroup_class_with_category'", "TypeError: unhashable type: 'AbsoluteOrder_with_category'", "TypeError: unhashable type: 'CartanType_affine_with_superclass'", "TypeError: unhashable type: 'CartesianProduct_with_category.element_class'", "TypeError: unhashable type: 'ChainComplex_class_with_category'", "TypeError: unhashable type: 'ClassGroup_with_category'", "TypeError: unhashable type: 'CompositeConstructionFunctor'", "TypeError: unhashable type: 'CrystalOfAlcovePaths_with_category.element_class'", "TypeError: unhashable type: 'CycleIndexSeriesRing_class_with_category'", "TypeError: unhashable type: 'CyclicPermutationGroup_with_category'", "TypeError: unhashable type: 'DihedralGroup_with_category'", "TypeError: unhashable type: 'EisensteinExtensionFieldCappedRelative_with_category'", "TypeError: unhashable type: 'EisensteinExtensionRingCappedAbsolute_with_category'", "TypeError: unhashable type: 'EisensteinExtensionRingCappedRelative_with_category'", "TypeError: unhashable type: 'EisensteinExtensionRingFixedMod_with_category'", "TypeError: unhashable type: 'FpT_with_category'", "TypeError: unhashable type: 'FractionField_1poly_field_with_category'", "TypeError: unhashable type: 'FractionField_generic_with_category'", "TypeError: unhashable type: 'Gamma0_class_with_category'", "TypeError: unhashable type: 'Gamma1_class_with_category'", "TypeError: unhashable type: 'GammaH_class_with_category'", "TypeError: unhashable type: 'HammingCode_with_category'", "TypeError: unhashable type: 'HyperbolicModelPD_with_category.element_class'", "TypeError: unhashable type: 'HyperellipticCurve_g2_rational_field_with_category'", "TypeError: unhashable type: 'HyperellipticCurve_rational_field_with_category'", "TypeError: unhashable type: 'IdealMonoid_c_with_category'", "TypeError: unhashable type: 'InfinitePolynomialFunctor'", "TypeError: unhashable type: 'KleinFourGroup_with_category'", "TypeError: unhashable type: 'LabelledBinaryTrees_with_category.element_class'", "TypeError: unhashable type: 'LaurentPolynomialRing_mpair_with_category'", "TypeError: unhashable type: 'LaurentPolynomialRing_univariate_with_category'", "TypeError: unhashable type: 'MPolynomialRing_polydict_domain_with_category'", "TypeError: unhashable type: 'MPolynomialRing_polydict_with_category'", "TypeError: unhashable type: 'MPolynomial_polydict'", "TypeError: unhashable type: 'ModularSymbolsAmbient_wtk_eps_with_category'", "TypeError: unhashable type: 'MultivariateProduct_with_category.element_class'", "TypeError: unhashable type: 'OverconvergentModularFormsSpace_with_category'", "TypeError: unhashable type: 'Partitions_with_constraints_with_category'", "TypeError: unhashable type: 'PolynomialQuotientRing_field_with_category'", "TypeError: unhashable type: 'PolynomialQuotientRing_generic_with_category'", "TypeError: unhashable type: 'ProjectiveSpace_rational_field_with_category'", "TypeError: unhashable type: 'QuaternionAlgebra_ab_with_category'", "TypeError: unhashable type: 'QuaternionFractionalIdeal_rational'", "TypeError: unhashable type: 'RelativeOrder_with_category'", "TypeError: unhashable type: 'SL2Z_class_with_category'", "TypeError: unhashable type: 'Subsets_sk_with_category'", "TypeError: unhashable type: 'SymbolicConstantsSubring_with_category'", "TypeError: unhashable type: 'SymmetricGroup_with_category'", "TypeError: unhashable type: 'ToricVariety_field_with_category'", "TypeError: unhashable type: 'UnivariateProduct_with_category.element_class'", "TypeError: unhashable type: 'UnramifiedExtensionFieldCappedRelative_with_category'", "TypeError: unhashable type: 'UnramifiedExtensionRingCappedAbsolute_with_category'", "TypeError: unhashable type: 'UnramifiedExtensionRingCappedRelative_with_category'", "TypeError: unhashable type: 'UnramifiedExtensionRingFixedMod_with_category'", "TypeError: unhashable type: 'pAdicAutomorphicForms_with_category'", "TypeError: unhashable type: 'sage.rings.padics.qadic_flint_CR.qAdicCappedRelativeElement'"]
comment:15 Changed 4 years ago by
Note that the changes (taken from comment:2)

src/sage/groups/abelian_gps/abelian_group.py
diff git a/src/sage/groups/abelian_gps/abelian_group.py b/src/sage/groups/abelian_gps/abelian_group.py index e19199b949..bf6fe5dc2c 100644
a b class AbelianGroup_class(UniqueRepresentation, AbelianGroupBase): 553 553 cat = cat.Infinite() 554 554 AbelianGroupBase.__init__(self, category=cat) 555 555 556 __hash__ = UniqueRepresentation.__hash__ 557 556 558 def is_isomorphic(left, right): 557 559 """ 558 560 Check whether ``left`` and ``right`` are isomorphic 
src/sage/groups/perm_gps/permgroup_named.py
diff git a/src/sage/groups/perm_gps/permgroup_named.py b/src/sage/groups/perm_gps/permgroup_named.py index da1774e96c..54fa034b4a 100644
a b class PermutationGroup_unique(CachedRepresentation, PermutationGroup_generic): 149 149 """ 150 150 return super(CachedRepresentation, self).__eq__(other) 151 151 152 __hash__ = CachedRepresentation.__hash__ 153 152 154 153 155 class PermutationGroup_symalt(PermutationGroup_unique): 154 156 """
fix many Python 3 doctest failures in sage/homology
. I don't know if this is the correct approach, or perhaps there is something more systematic to make hashes inherit even when __eq__
is defined.
comment:16 Changed 4 years ago by
If you're using the __hash__
of UniqueRepresentation
but not its __eq__
, then you're doing it wrong. So this might indicate an actual bug.
comment:17 followup: 19 Changed 4 years ago by
That class has the line
__eq__ = is_isomorphic
so that generator names (for example) don't affect equality. (is_isomorphic
just checks whether the elementary divisors match up.) We could define __hash__
correspondingly. For the simplicial complex code, the important thing (I think) is that the class of abelian groups is hashable. I assume that any reasonable hash function will work.
(I also don't know how or why the design decisions for AbelianGroup_class
were made.)
comment:18 Changed 4 years ago by
Confirmed:

src/sage/groups/abelian_gps/abelian_group.py
diff git a/src/sage/groups/abelian_gps/abelian_group.py b/src/sage/groups/abelian_gps/abelian_group.py index e19199b949..62a5e25edb 100644
a b class AbelianGroup_class(UniqueRepresentation, AbelianGroupBase): 553 553 cat = cat.Infinite() 554 554 AbelianGroupBase.__init__(self, category=cat) 555 555 556 def __hash__(self): 557 return hash(self.elementary_divisors()) 558 556 559 def is_isomorphic(left, right): 557 560 """ 558 561 Check whether ``left`` and ``right`` are isomorphic
works just as well, at least as far as the homology code is concerned.
comment:19 Changed 4 years ago by
Replying to jhpalmieri:
That class has the line
__eq__ = is_isomorphicso that generator names (for example) don't affect equality.
This is different from most other things in Sage though. For example
sage: GF(9, 'a') == GF(9, 'b') False sage: QQ['x'] == QQ['y'] False
I'm not saying that this is necessarily a bug. However, if you can change __eq__
without breaking anything else, I would do that instead of changing __hash__
.
comment:20 Changed 4 years ago by
I opened #25935 for AbelianGroup_class
. Please continue the discussion there.
comment:22 Changed 4 years ago by
Milestone:  sage8.2 → sagepending 

Added one for HyperellipticCurve_generic
in #25946.
comment:23 Changed 4 years ago by
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comment:36 Changed 4 years ago by
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Good to know is that there is a metaclass
InheritComparison
which is supposed to fix that problem.