Python 局部变量'；Veh#u C2X#u属性'；在分配源之前引用？

我试图从一个微型模拟软件PTV VISSIM运行这个脚本。并且得到了这个错误。分配源之前引用的局部变量“Veh_C2X_attributes”？？在我的脚本中，我使用列表理解创建了一个名为“Veh_C2X_attributes”的列表。任何有关这方面的帮助都将不胜感激。谢谢

剧本

def Init():
    #Global Parameters
    global distDistr
    global Vehicle_Type_C2X_no_message
    global Vehicle_Type_C2X_HasCurrentMessage
    Veh_attributes = None

    distDistr = 1 # number of Distance distribution used for sending out a C2X message
    Vehicle_Type_C2X_no_message = '101' # number of C2X vehicle type (no active message) has to be a string!
    Vehicle_Type_C2X_HasCurrentMessage = '102' # number of C2X vehicle type with active message has to be a string!
    return



def Main():
    # Get several attributes of all vehicles:
    Veh_attributes = Vissim.Net.Vehicles.GetMultipleAttributes(('Pos', 'VehType', 'No'))
    if len(Veh_attributes) > 0: # Check if there are any vehicles in the network:
       # Filter by VehType C2X:
        Veh_C2X_attributes = None
        Veh_C2X_attributes = [item for item in Veh_attributes if item[1] == Vehicle_Type_C2X_no_message or item[1] == Vehicle_Type_C2X_HasCurrentMessage]    #Getting Error here
#Check if the Vehicle is in the range
    for C2X_Veh in range(len(Veh_C2X_attributes)):
        if Veh_C2X_attributes[C2X_Veh][0]==300:
            Veh_sending_Msg = Vissim.Net.Vehicles.ItemByKey(Veh_C2X_attributes[C2X_Veh][3])
            Coord_Veh = Veh_sending_Msg.AttValue('CoordFront') # reading the world coordinates (x y z) of the vehicle
            PositionXYZ = Coord_Veh.split(" ")
            Pos_Veh_SM = Veh_sending_Msg.AttValue('Pos') # relative position on the current link
            Veh_sending_Msg.SetAttValue('C2X_HasCurrentMessage', 1)
            Veh_sending_Msg.SetAttValue('C2X_SendingMessage', 1)
            Veh_sending_Msg.SetAttValue('C2X_MessageOrigin', Pos_Veh_SM)
            # Getting vehicles which receive the message:
            Veh_Rec_Message = Vissim.Net.Vehicles.GetByLocation(PositionXYZ[0], PositionXYZ[1], distDistr)
    return

如果len（Veh_属性）>0:失败，则

的
车辆C2X_属性
未定义

确保这一点的一种方法是在
if len（Veh_属性）>0:
中放入
print
，以检查是否正在执行该条件

另外，更好的做法是在之前定义
Veh_C2X_属性

例如：

如果有人能说服我为什么投票被否决，我会删除/编辑这个答案。
def Main():
    # Get several attributes of all vehicles:
    Veh_C2X_attributes = [] # this will prevent code from failing
    Veh_attributes = Vissim.Net.Vehicles.GetMultipleAttributes(('Pos', 'VehType', 'No'))
    if len(Veh_attributes) > 0: # Check if there are any vehicles in the network:
       # Filter by VehType C2X:
        Veh_C2X_attributes = [item for item in Veh_attributes if item[1] == Vehicle_Type_C2X_no_message or item[1] == Vehicle_Type_C2X_HasCurrentMessage]    #Getting Error here
#Check if the Vehicle is in the range
    for C2X_Veh in range(len(Veh_C2X_attributes)):
        if Veh_C2X_attributes[C2X_Veh][0]==300:
            Veh_sending_Msg = Vissim.Net.Vehicles.ItemByKey(Veh_C2X_attributes[C2X_Veh][3])
            Coord_Veh = Veh_sending_Msg.AttValue('CoordFront') # reading the world coordinates (x y z) of the vehicle
            PositionXYZ = Coord_Veh.split(" ")
            Pos_Veh_SM = Veh_sending_Msg.AttValue('Pos') # relative position on the current link
            Veh_sending_Msg.SetAttValue('C2X_HasCurrentMessage', 1)
            Veh_sending_Msg.SetAttValue('C2X_SendingMessage', 1)
            Veh_sending_Msg.SetAttValue('C2X_MessageOrigin', Pos_Veh_SM)
            # Getting vehicles which receive the message:
            Veh_Rec_Message = Vissim.Net.Vehicles.GetByLocation(PositionXYZ[0], PositionXYZ[1], distDistr)
    return