How to use the constructs.Variable function in constructs

def get_affine_var_and_param_coeff(expr):
    expr = Value.numericToValue(expr)

    if (not isAffine(expr) or \
            isinstance(expr, Value) or \
            is_constant_expr(expr)):
        return {}
    elif (isinstance(expr, constructs.Variable)):
        return {expr: 1}
    elif (isinstance(expr, AbstractBinaryOpNode)):
        coeff = {}
        left_coeff = get_affine_var_and_param_coeff(expr.left)
        right_coeff = get_affine_var_and_param_coeff(expr.right)
        if (expr.op == '+'):
            coeff = dict((n, left_coeff.get(n, 0) + right_coeff.get(n, 0)) \
                             for n in set(left_coeff) | set(right_coeff))
        elif (expr.op == '-'):
            coeff = dict((n, left_coeff.get(n, 0) - right_coeff.get(n, 0)) \
                             for n in set(left_coeff) | set(right_coeff))
        elif (expr.op == '*'):
            left_is_constant = is_constant_expr(expr.left, affine=True)
            right_is_constant = is_constant_expr(expr.right, affine=True)
            #sanity check should be true if the expression is affine
            assert(not (left_is_constant and right_is_constant))

def getType(expr):
    expr = Value.numericToValue(expr)
    assert(isinstance(expr, AbstractExpression))
    if (isinstance(expr, Value)):
        return expr.typ
    elif (isinstance(expr, constructs.Variable)):
        return expr.typ
    elif (isinstance(expr, constructs.Reference)):
        return expr.objectRef.typ
    elif (isinstance(expr, AbstractBinaryOpNode)):
        left_type = getType(expr.left)
        right_type = getType(expr.right)
        return result_type(left_type, right_type)
    elif (isinstance(expr, AbstractUnaryOpNode)):
        return getType(expr.child)
    elif (isinstance(expr, constructs.Cast)):
        return expr.typ
    elif (isinstance(expr, constructs.Select)):
        true_type = getType(expr.trueExpression)
        false_type = getType(expr.falseExpression)
        assert true_type == false_type
        return true_type