如何排除负数？答案

【问题标题】：How can I exclude negative numbers?如何排除负数？
【发布时间】：2019-04-16 22:07:58
【问题描述】：

我不确定如何防止负数影响最终计算。

我不知道还能尝试什么。

for month in months:
    rainfall_answer = int(input("What was the rainfall in {}? ".format(month)))
    if rainfall_answer < 0:
        print("Input must be positive.")
        rainfall_answer = int(input("What was the rainfall in {}? ".format(month)))
    elif rainfall_answer > 0:
        rainfall.append(rainfall_answer)

我希望无效输入不会包含在最终结果中。

【问题讨论】：

Asking the user for input until they give a valid response的可能重复

标签： python list loops

【解决方案1】：

您可以使用 while 循环来循环输入，还需要使用 try except 块来处理和引发异常，在这种情况下不包括负数

for month in months:
  while True:
    try:
        rainfall_answer = int(input("What was the rainfall in {}? ".format(month)))
        if rainfall_answer < 0:
            raise ValueError
        break
    except ValueError:
        print ("Input must be positive")
rainfall.append(rainfall_answer)

【讨论】：

【解决方案2】：

如果我理解正确，您可以使用while 循环反复提示用户，直到输入为非负数：

for month in months:
    rainfall_answer = int(input("What was the rainfall in {}? ".format(month)))
    while rainfall_answer < 0:
        print("Input must be positive.")
        rainfall_answer = int(input("What was the rainfall in {}? ".format(month)))

    rainfall.append(rainfall_answer)

【讨论】：

【解决方案3】：

您快到了，您可以使用的一个技巧是将rainfall_answer 设置为负（无效）值，然后您可以重复input 读取，直到您在rainfall_answer 中获得正值：

for month in months:
    rainfall_answer = -1
    while rainfall_answer < 0:
        rainfall_answer = int(input("What was the rainfall in {}? ".format(month)))
    rainfall.append(rainfall_answer)

【讨论】：

【解决方案4】：

你需要循环输入。

for month in months:
    while True:
        rainfall_answer = int(input("What was the rainfall in {}? ".format(month)))
        if rainfall_answer >= 0:
            break  # exit while loop because you got valid input
        else:
            print('Input must be positive')
    rainfall.append(rainfall_answer)

【讨论】：