How to use the pyscipopt.scip.Expr function in PySCIPOpt

def test_degree(model):
    m, x, y, z = model
    expr = Expr()
    assert expr.degree() == 0

    expr = Expr() + 3.0
    assert expr.degree() == 0

    expr = x + 1
    assert expr.degree() == 1

    expr = x*x + y - 2
    assert expr.degree() == 2

    expr = (x + 1)*(y + 1)*(x - 1)
    assert expr.degree() == 3

def test_degree(model):
    m, x, y, z = model
    expr = Expr()
    assert expr.degree() == 0

    expr = Expr() + 3.0
    assert expr.degree() == 0

    expr = x + 1
    assert expr.degree() == 1

    expr = x*x + y - 2
    assert expr.degree() == 2

    expr = (x + 1)*(y + 1)*(x - 1)
    assert expr.degree() == 3

def test_upgrade(model):
    m, x, y, z = model
    expr = x + y
    assert isinstance(expr, Expr)
    expr += exp(z)
    assert isinstance(expr, GenExpr)

    expr = x + y
    assert isinstance(expr, Expr)
    expr -= exp(z)
    assert isinstance(expr, GenExpr)

    expr = x + y
    assert isinstance(expr, Expr)
    expr /= x
    assert isinstance(expr, GenExpr)

    expr = x + y
    assert isinstance(expr, Expr)
    expr *= sqrt(x)

def test_upgrade(model):
    m, x, y, z = model
    expr = x + y
    assert isinstance(expr, Expr)
    expr += exp(z)
    assert isinstance(expr, GenExpr)

    expr = x + y
    assert isinstance(expr, Expr)
    expr -= exp(z)
    assert isinstance(expr, GenExpr)

    expr = x + y
    assert isinstance(expr, Expr)
    expr /= x
    assert isinstance(expr, GenExpr)

    expr = x + y
    assert isinstance(expr, Expr)
    expr *= sqrt(x)
    assert isinstance(expr, GenExpr)

    expr = x + y
    assert isinstance(expr, Expr)
    expr **= 1.5

assert expr[x] == 1.0
    assert expr[y] == 1.0
    assert expr[z] == 0.0

    expr = -x
    assert isinstance(expr, Expr)
    assert expr[x] == -1.0
    assert expr[y] ==  0.0

    expr = x*4
    assert isinstance(expr, Expr)
    assert expr[x] == 4.0
    assert expr[y] == 0.0

    expr = 4*x
    assert isinstance(expr, Expr)
    assert expr[x] == 4.0
    assert expr[y] == 0.0

    expr = x + y + x
    assert isinstance(expr, Expr)
    assert expr[x] == 2.0
    assert expr[y] == 1.0

    expr = x + y - x
    assert isinstance(expr, Expr)
    assert expr[x] == 0.0
    assert expr[y] == 1.0

    expr = 3*x + 1.0
    assert isinstance(expr, Expr)
    assert expr[x] == 3.0

def test_operations_linear(model):
    m, x, y, z = model
    expr = x + y
    assert isinstance(expr, Expr)
    assert expr[x] == 1.0
    assert expr[y] == 1.0
    assert expr[z] == 0.0

    expr = -x
    assert isinstance(expr, Expr)
    assert expr[x] == -1.0
    assert expr[y] ==  0.0

    expr = x*4
    assert isinstance(expr, Expr)
    assert expr[x] == 4.0
    assert expr[y] == 0.0

    expr = 4*x
    assert isinstance(expr, Expr)