Add test for scalar * Expr multiplication

Add an assertion in tests/test_expr.py to verify left-side scalar multiplication works: assert str(2.0 * (x + y)) == "Expr({Term(x): 2.0, Term(y): 2.0})". This ensures that multiplying an Expr by a scalar on the left yields the same result and string representation as Expr * scalar.

Author: Zeroto521

src/pyscipopt/expr.pxi

@@ -296,7 +296,7 @@ cdef class Expr:
             while PyDict_Next(self.terms, &pos1, &k1_ptr, &v1_ptr):
                 res[<Term>k1_ptr] = <double>(<object>v1_ptr) * coef
             return Expr(res)
-    
+
         elif isinstance(other, Expr):
             while PyDict_Next(self.terms, &pos1, &k1_ptr, &v1_ptr):
                 pos2 = <Py_ssize_t>0

tests/test_expr.py

@@ -226,6 +226,7 @@ def test_mul():
 
     # test Expr * number
     assert str((x + y) * 2.0) == "Expr({Term(x): 2.0, Term(y): 2.0})"
+    assert str(2.0 * (x + y)) == "Expr({Term(x): 2.0, Term(y): 2.0})"
 
     # test Expr * Expr
     assert str(Expr({CONST: 1.0}) * x) == "Expr({Term(x): 1.0})"