可以弄清楚为什么我的entry（）小部件返回null

Question

我一直在尝试将数据从函数中的输入框传递到另一个函数，但是entry.get（）函数似乎什么也没返回。这是我的代码的一部分。谢谢大家

def cubedim():

    dimensionframeclear()
    length = 0.0
    length1label = Label(DimensionFrame, text="Length", font=7)
    length1label.grid(row=1, column=0)
    cubelength = Entry(DimensionFrame, textvariable=length)
    cubelength.grid(row=1,column=1, padx=5)

    calculatebutton = Button(DimensionFrame, text= "Calculate")
    calculatebutton.grid(row=1,column=4)
    return length

def totalamount():
    

    if var1.get() == 1:
        length = cubedim()
        dimensionofgift = length * length
    
    if var5.get() == 1:
        paperprice = 0.4
    elif var5.get() == 2:
        paperprice = 0.75

    itembow = int(var3.get())
    itemcard = int(var4.get())
    characterlength = len(CardMsg.get())
    if itembow == 1:
        pricebow = 1.5
    else:
        pricebow = 0
    if itemcard == 1:
        pricecard = 0.5
    else:
        pricecard = 0
    subtotal = dimensionofgift * paperprice + pricecard + pricebow + (characterlength*0.5)
    return subtotal