abs(abs(x)) should return abs(x) rather than abs(abs(x))

CHANGELOG.md

@@ -22,6 +22,7 @@
 - Speed up MatrixExpr.add.reduce via quicksum
 - Speed up np.ndarray(..., dtype=np.float64) @ MatrixExpr
 - MatrixExpr and MatrixExprCons use `__array_ufunc__` protocol to control all numpy.ufunc inputs and outputs
+- Return itself for abs to UnaryExpr(Operator.fabs)
 ### Removed
 
 ## 6.0.0 - 2025.xx.yy

src/pyscipopt/expr.pxi

@@ -45,9 +45,10 @@
 import math
 from typing import TYPE_CHECKING
 
-from pyscipopt.scip cimport Variable, Solution
 from cpython.dict cimport PyDict_Next
+from cpython.object cimport Py_TYPE
 from cpython.ref cimport PyObject
+from pyscipopt.scip cimport Variable, Solution
 
 import numpy as np
 
@@ -647,6 +648,20 @@ cdef class GenExpr:
         '''returns operator of GenExpr'''
         return self._op
 
+    cdef GenExpr copy(self, bool copy = True):
+        cdef object cls = <type>Py_TYPE(self)
+        cdef GenExpr res = cls.__new__(cls)
+        res._op = self._op
+        res.children = self.children.copy() if copy else self.children
+        if cls is SumExpr:
+            (<SumExpr>res).constant = (<SumExpr>self).constant
+            (<SumExpr>res).coefs = (<SumExpr>self).coefs.copy() if copy else (<SumExpr>self).coefs
+        if cls is ProdExpr:
+            (<ProdExpr>res).constant = (<ProdExpr>self).constant
+        elif cls is PowExpr:
+            (<PowExpr>res).expo = (<PowExpr>self).expo
+        return res
+
 
 # Sum Expressions
 cdef class SumExpr(GenExpr):
@@ -736,6 +751,11 @@ cdef class UnaryExpr(GenExpr):
         self.children.append(expr)
         self._op = op
 
+    def __abs__(self) -> UnaryExpr:
+        if self._op == "abs":
+            return <UnaryExpr>self.copy()
+        return UnaryExpr(Operator.fabs, self)
+
     def __repr__(self):
         return self._op + "(" + self.children[0].__repr__() + ")"
 

src/pyscipopt/scip.pyi

@@ -377,7 +377,7 @@ class GenExpr:
     def __init__(self) -> None: ...
     def degree(self) -> Incomplete: ...
     def getOp(self) -> Incomplete: ...
-    def __abs__(self) -> Incomplete: ...
+    def __abs__(self) -> GenExpr: ...
     def __add__(self, other: Incomplete) -> Incomplete: ...
     def __eq__(self, other: object) -> bool: ...
     def __ge__(self, other: object) -> bool: ...
@@ -2161,9 +2161,9 @@ class Term:
     def __lt__(self, other: object) -> bool: ...
     def __ne__(self, other: object) -> bool: ...
 
-@disjoint_base
 class UnaryExpr(GenExpr):
     def __init__(self, *args: Incomplete, **kwargs: Incomplete) -> None: ...
+    def __abs__(self) -> GenExpr: ...
 
 @disjoint_base
 class VarExpr(GenExpr):

tests/test_expr.py

@@ -218,3 +218,11 @@ def test_getVal_with_GenExpr():
 
     with pytest.raises(ZeroDivisionError):
         m.getVal(1 / z)
+
+
+def test_abs_abs_expr():
+    m = Model()
+    x = m.addVar(name="x")
+
+    # should print abs(x) not abs(abs(x))
+    assert str(abs(abs(x))) == str(abs(x))