Python 3.x 错误检查：比如检查负数，或者输入非数字。

我是新手，只是不知道应该如何/在哪里使用try和，除非用户输入负数或字符串。

可以这样尝试：

weight=input('What is your weight?')
age=input('What is your age?')
w=int(weight)
a=int(weight)
if (a<=10 and w<80):
  print('This person needs to ride the black roller coaster')
if (a<=10 and 80<=w<=200):
  print('This person needs to ride the green roller coaster')
if (a<=10 and w>200):
  print('This person needs to ride the yellow roller coaster')
if (10<a<=20 and w<80):
  print('This person needs to ride the silver roller coaster')
if (10<a<=20 and 80<=w<=200):
  print('This person needs to ride the red roller coaster')
if (10<a<=20 and w>200):
  print('This person needs to ride the purple roller coaster')
else:
  print('This person needs to ride the pink roller coaster')

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理想的结果是什么？如果用户输入是在什么情况下，则仅显示一条错误消息，如“Entry必须是大于0的数字”？

def checkValue():
while True:
    try:
        global a, w
        a = int(input("What's your age? ").strip())
        w = int(input("What's your weight? ").strip())
    except ValueError as e:
        print("This is not a number. Try again.")
        continue
    if a <= 0 and w <= 0:
        print("Enter value lager than 0.")
        continue
    else:
        break
    return a, w

checkValue ()