BUG: Expr.__array_ufunc__ can't handle 0-dim array

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Unreleased
 ### Added
 ### Fixed
+- `Expr.__array_ufunc__` can't handle 0-dim array
 ### Changed
 ### Removed
 

src/pyscipopt/expr.pxi

@@ -203,16 +203,24 @@ cdef class ExprLike:
             )
 
         if method == "__call__":
-            if arrays := [a for a in args if isinstance(a, np.ndarray)]:
+            if arrays := [a for a in args if isinstance(a, np.ndarray) and a.ndim >= 1]:
                 if any(a.dtype.kind not in "fiub" for a in arrays):
                     return NotImplemented
                 # If the np.ndarray is of numeric type, all arguments are converted to
                 # MatrixExpr or MatrixGenExpr and then the ufunc is applied.
                 return ufunc(*[_ensure_matrix(a) for a in args], **kwargs)
 
-            # Convert `np.generic` to native Python types to stop __array_ufunc__
-            # recursion from `np.generic + MatrixExpr`.
-            args = [a.item() if isinstance(a, np.generic) else a for a in args]
+            # Convert `np.generic` and 0-dim `np.ndarray` to native Python types to stop
+            # __array_ufunc__ recursion from `np.generic + MatrixExpr/Expr`.
+            args = [
+                a.item()
+                if (
+                    isinstance(a, np.generic)
+                    or (isinstance(a, np.ndarray) and a.ndim == 0)
+                )
+                else a
+                for a in args
+            ]
 
             if ufunc is np.add:
                 return args[0] + args[1]

tests/test_expr.py

@@ -328,6 +328,18 @@ def test_binary_ufunc(model):
     assert str(np.greater_equal(a, x)) == "[ExprCons(Expr({Term(x): 1.0}), None, 2.0)]"
 
 
+def test_np_generic_cmp_with_expr():
+    # test #1218
+    m = Model()
+    x = m.addVar(name="x")
+    value = np.float64(5.0)
+
+    assert str(x <= -value) == "ExprCons(Expr({Term(x): 1.0}), None, -5.0)"
+    assert str(x <= value ) == "ExprCons(Expr({Term(x): 1.0}), None, 5.0)"
+    assert str(-value <= x) == "ExprCons(Expr({Term(x): 1.0}), -5.0, None)"
+    assert str(value <= x) == "ExprCons(Expr({Term(x): 1.0}), 5.0, None)"
+
+
 def test_mul():
     m = Model()
     x = m.addVar(name="x")