Appending a list to another list returns an empty list-CodePudding

I'm trying to create a list that stores user input to be later manipulated. However when the User inputs names into the temporary list, it updates showing that the nameList has been updated, but when i add the nameList to the concernList, it does not add anything but an empty List! Empty List

 concernList = []
nameList = []



def nameLoop():
    global concernList
    global nameList
    first = input("First Name: ")
    nameList.append(first)
    print(nameList)
    middle = input("Middle Initial: ")
    nameList.append(middle)
    print(nameList)
    last = input("Last Name: ")
    nameList.append(last)
    print(nameList)
    concernList.append(nameList)
    nameList.clear()

def siteMonitor():
    pass


nameLoop()

while True:
    newConcernInput = input("Add Another Concern? (y/n)")
    if (newConcernInput.lower() == 'y'):
        nameLoop()
        print("Type 'q' to stop adding concerns. ")

    if (newConcernInput.lower() == 'n'):
        monitorInput = input("Begin Background Monitoring? (y/n)")
        if (monitorInput == 'y'):
            siteMonitor()
        else:
            pass

    if (newConcernInput.lower() == 'q'):
        break

    for count in range(0, len(nameList)):
        pass

    print(concernList)
    print("Added To Concern List.")

CodePudding user response：

concernList.append(nameList) doesn't create a second list - the newly added element is just a reference to the original list (related). This means that nameList.clear() will delete the contents of the same list that you just appended to concernList.

However, I don't see the need for a global nameList in the first place. This is how I would rewrite the code:

concernList = []
nameList = []

def nameLoop():
    first = input("First Name: ")
    middle = input("Middle Initial: ")
    last = input("Last Name: ")
    return [first, middle, last]

def siteMonitor():
    pass

nameList = nameLoop()
concernList.append(nameList)

while True:
    newConcernInput = input("Add Another Concern? (y/n)")
    if newConcernInput.lower() == 'y':
        nameList = nameLoop()
        concernList.append(nameList)
        print("Type 'q' to stop adding concerns. ")
    
    if newConcernInput.lower() == 'n':
        monitorInput = input("Begin Background Monitoring? (y/n)")
        if monitorInput == 'y':
            siteMonitor()
        else:
            pass
    
    if newConcernInput.lower() == 'q':
        break
    
    for count in range(0, len(nameList)):
        pass
    
    print(concernList)
    print("Added To Concern List.")