Python3.8中的“NameError：名称'day_time'未定义”错误[重复]

Question

我正在制作一个程序，它可以根据输入的时间告诉一天中的哪个部分。

我的代码：

user_day = input("What's the time? ")

if user_day >= 20 and user_day <= 24:
    day_time = "Night"

elif user_day >= 24 and user_day <= 12:
    day_time = "Morning"

elif user_day >= 12 and user_day >= 17:
    day_time = "Noon"

elif user_day >= 17 and user_day >= 20:
    day_time = "Evening"

但我收到此错误：

if day_time == 1 and user_weather == plus:
NameError: name 'day_time' is not defined

请帮帮我。

Answer 1

如果你想稍后使用它，你需要在 if 块的上下文之外声明day_time。

像这样，例如：

user_day = input("What's the time? ")

day_time = None

if user_day >= 20 and user_day <= 24:
    day_time = "Night"

elif user_day >= 24 and user_day <= 12:
    day_time = "Morning"

elif user_day >= 12 and user_day >= 17:
    day_time = "Noon"

elif user_day >= 17 and user_day >= 20:
    day_time = "Evening"

Answer 2

• 问题是，user_day 在作为输入输入时是一个字符串。
  • 因为它是一个字符串，它不满足任何条件，因此，day_time 保持未定义。
    • 将输入包装在try-except 块中以检查输入是否为正确的数据类型。在这种情况下，str 类型可以转换为int 或float。
  • 必须将其转换为 int 或 float，具体取决于您是仅接受小时数还是小数小时数。
• user_day 应该在 while True 循环中继续请求时间，直到收到有效的数字输入。
• 最后，对于这种情况，通过正确地从小到大对条件进行排序，可以更有效地编写代码。
  • user_day 将逐渐下降到正确的条件。

while True:
    try:
        user_day = int(input("What's the hour on a 24-hour scale? "))
    except ValueError:  # checks for the correct data type; maybe someone will spell the hour
        print('Please enter the hour as a numeric value')
    
    if (user_day >= 24) or (user_day < 0):  # 24 and over or less than 0 are invalid times
        print('Please enter a valid time')
    else:
        break  # break when there's valid input

if user_day < 12:
    day_time = 'Morning'
elif user_day < 17:
    day_time = 'Noon'
elif user_day < 20:
    day_time = 'Evening'
else:
    day_time = 'Night'
    
print(day_time)

使用np.digitize

• 返回每个输入值所属的 bin 的索引。
• 使用np.digitize返回的值来索引day_time中的正确值

import numpy as np

while True:
    try:
        user_day = int(input("What's the hour on a 24-hour scale? "))
    except ValueError:  # checks for the correct data type; maybe someone will spell the hour
        print('Please enter the hour as a numeric value')
    
    if (user_day >= 24) or (user_day < 0):  # 24 and over or less than 0 are invalid times
        print('Please enter a valid time')
    else:
        break  # break when there's valid input

day_time = ['Morning', 'Evening', 'Noon', 'Night']
idx = np.digitize(user_day, bins=[12, 17, 20])
    
print(day_time[idx])

Answer 3

您需要在else 语句中定义day_time，这样当现有条件都不满足时，day_time 仍然有一个值。

此外，您需要将用户的输入转换为整数，然后才能在其上使用带有字符串的<、> 等运算符：

user_day = int(input("What's the time? "))

if user_day >= 20 and user_day <= 24:
    day_time = "Night"

elif user_day >= 24 and user_day <= 12:
    day_time = "Morning"

elif user_day >= 12 and user_day >= 17:
    day_time = "Noon"

elif user_day >= 17 and user_day >= 20:
    day_time = "Evening"

else:
    day_time = "Unknown"