#12876: Fix element and parent classes of Hom categories to be abstract, and
simplify the Hom logic.
-------------------------------------+--------------------------------------
Reporter: nthiery | Owner: nthiery
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.1
Component: categories | Resolution:
Keywords: categories, Hom | Work issues: Fix ring_refcount_dict
problem
Report Upstream: N/A | Reviewers: Simon King
Authors: Nicolas M. Thiéry | Merged in:
Dependencies: #12875, #12877 | Stopgaps:
-------------------------------------+--------------------------------------
Comment (by SimonKing):
Here is the rejection:
{{{
#!diff
--- homset.py
+++ homset.py
@@ -165,43 +203,27 @@ def Hom(X, Y, category=None):
if H.domain() is X and H.codomain() is Y:
return H
- try:
- return X._Hom_(Y, category)
- except (AttributeError, TypeError):
- pass
-
cat_X = X.category()
cat_Y = Y.category()
if category is None:
- category = cat_X._meet_(cat_Y)
- elif isinstance(category, Category):
- if not cat_X.is_subcategory(category):
- raise TypeError, "%s is not in %s"%(X, category)
- if not cat_Y.is_subcategory(category):
- raise TypeError, "%s is not in %s"%(Y, category)
- else:
+ return Hom(X,Y,category=cat_X._meet_(cat_Y))
+ if not isinstance(category, Category):
raise TypeError, "Argument category (= %s) must be a
category."%category
- # Now, as the category may have changed, we try to find the hom set
in the cache, again:
- key = (X,Y,category)
- if _cache.has_key(key):
- H = _cache[key]()
- if H:
- # Are domain or codomain breaking the unique parent
condition?
- if H.domain() is X and H.codomain() is Y:
- return H
-
- # coercing would be incredibly annoying, since the domain and
codomain
- # are totally different objects
- #X = category(X); Y = category(Y)
+ if not cat_X.is_subcategory(category):
+ raise TypeError, "%s is not in %s"%(X, category)
+ if not cat_Y.is_subcategory(category):
+ raise TypeError, "%s is not in %s"%(Y, category)
# construct H
# Design question: should the Homset classes get the category or the
homset category?
# For the moment, this is the category, for compatibility with the
current implementations
# of Homset in rings, schemes, ...
- H = category.hom_category().parent_class(X, Y, category = category)
-
- ##_cache[key] = weakref.ref(H)
- _cache[(X, Y, category)] = weakref.ref(H)
+ from sets_cat import Sets
+ try:
+ H = X._Hom_(Y, category)
+ except (AttributeError, TypeError):
+ H = Homset(X, Y, category = category)
+ _cache[key] = weakref.ref(H)
return H
def hom(X, Y, f):
}}}
Why do you import Sets (new line 221)?
Do I understand correctly: If Hom receives None as category, then you
determine the category as the meet of the categories of domain and
codomain, and call Hom again. Did you test that the calling overhead does
not matter?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12876#comment:17>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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