Python將一個空列表更改爲一個整數

Question

所以我的問題是編寫一個函數語句（），它將浮點數字列表作爲輸入，其中正數表示存款和負數表示從銀行賬戶。你的函數應該返回一個兩個浮點數的列表;第一個將是存款的總和，第二個（負數）將是提款的總和。

而我寫的似乎是將退出空列表更改爲值0，因此不允許附加功能工作。我想知道是否有一個原因蟒蛇這樣做，或者如果它只是一個奇怪的錯誤？

下面是引用代碼：

def statement(lst): 
"""returns a list of two numbers; the first is the sum of the 
    positive numbers (deposits) in list lst, and the second is 
    the sum of the negative numbers (withdrawals)""" 
deposits, withdrawals, final = [], [], [] 
for l in lst: 
    print(l) 
    if l < 0: 
     print('the withdrawals are ', withdrawals) # test 
     withdrawals.append(l) 
     print('the withdrawals are ', withdrawals) # test 
    else: 
     print('the deposits are', deposits) # test 
     deposits.append(l) 
     print('the deposits are', deposits) # test 
    withdrawals = sum(withdrawals) 
    deposits = sum(deposits) 
    final.append(deposits) 
    final.append(withdrawals) 

Answer 1

這些行：

withdrawals = sum(withdrawals) 
deposits = sum(deposits) 
final.append(deposits) 
final.append(withdrawals) 

需要被寫成：

final.append(sum(deposits)) 
final.append(sum(withdrawals)) 

否則，變量withdrawals和deposits將反彈到由sum返回的整數對象。換句話說，他們將不再引用這裏創建的列表對象：

deposits, withdrawals, final = [], [], []