Deprecated Term.ptrtuple and speed up Term.__eq__

[Zeroto521]

Term class has vartuple and ptrtuple. Both are variable containers, so it's duplicated.
Removing Term.ptrtuple could save about 50% memery.
Term.__eq__ is faster than the master branch when they differ. And having almost the same speed for the same Term.

Test item	Optimized before	Optimized after
Memery usage	15.77KB	7.91KB
Same Terms to compare	0.9245s	1.0219s
Different Terms to compare	0.3283s	0.0066s

from timeit import timeit
import sys

from pyscipopt import Model, quickprod


def memsize(obj):
    size_bytes = sys.getsizeof(obj) + sys.getsizeof(obj.vartuple)
    if hasattr(obj, "ptrtuple"):
        size_bytes += sys.getsizeof(obj.ptrtuple)

    if size_bytes < 1024:
        return f"{size_bytes}B"
    elif size_bytes < 1024**2:
        return f"{size_bytes / 1024:.2f}KB"
    return f"{size_bytes / 1024**2:.2f}MB"


m = Model()

n = 1_000
print(f"create 2 `Term` which have {n:,} vars each")
x = m.addMatrixVar(n)
e1 = quickprod(x.flat)
e2 = quickprod(x.flat)
t1 = next(iter(e1))
t2 = next(iter(e2))
print(t1 == t2)  # should be True
print(f"memory size: {memsize(t1)}")

y = m.addVar(name="y")
z = m.addVar(name="z")
t3 = next(iter(e1 * y))
t4 = next(iter(e2 * z))
print(t3 == t4)  # should be False

number = 100_000
print(f"repeat {number:,} times")
cost = timeit(lambda: t1 == t2, number=number)
print(f"XXX: {cost:.4f} seconds")

cost = timeit(lambda: t3 == t4, number=number)
print(f"XXX: {cost:.4f} seconds")

[Copilot]

Pull request overview

This pull request optimizes the Term class by removing the ptrtuple attribute and reimplementing __eq__ using C-level APIs. The changes aim to reduce memory usage by ~50% and improve comparison performance, particularly for different terms.

Changes:

• Removed Term.ptrtuple attribute to reduce memory footprint
• Optimized Term.__eq__ with identity checks, hash comparison, and C-level tuple access
• Added Variable.__hash__() method and made ptr() delegate to it for consistency

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/pyscipopt/scip.pyi	Removed ptrtuple attribute declaration from Term class type stub
src/pyscipopt/scip.pxi	Added __hash__() method to Variable class and refactored ptr() to call it
src/pyscipopt/expr.pxi	Removed ptrtuple attribute, replaced pointer-based sorting/hashing with hash-based approach, and optimized __eq__ implementation
CHANGELOG.md	Documented the removal of ptrtuple and performance improvements to __eq__

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[Zeroto521]

Variable.__hash__ is different from Expr. So it has to add __richcm__ by hand. Otherwise python can't find the comparison method

[Zeroto521]

hash(res.vartuple) reqires Variable.__hash__.