Python将一个空列表更改为一个整数

Question

所以我的问题是编写一个函数语句（），它将浮点数字列表作为输入，其中正数表示存款和负数表示从银行账户。你的函数应该返回一个两个浮点数的列表;第一个将是存款的总和，第二个（负数）将是提款的总和。

而我写的似乎是将退出空列表更改为值0，因此不允许附加功能工作。我想知道是否有一个原因蟒蛇这样做，或者如果它只是一个奇怪的错误？

下面是引用代码：

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

这些行：

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

需要被写成：

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

否则，变量withdrawals和deposits将反弹到由sum返回的整数对象。换句话说，他们将不再引用这里创建的列表对象：

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