Python if和elif不起作用，给出错误

Question

I'm new in Python and doing an online tutorial. I have an assignment that I can not accomplish. My problem is that when I run this code, the minimum variable stays the same to None and does not record the new value input.

maximum = None
minimum = None
while True:
    try:
        num2 = raw_input('Type here ')
        if num2 == 'done':break
        else:
            num = int(num2)
            if num <= minimum:
                minimum = num
                print minimum
            elif num >= maximum:
                maximum = num
                print maximum


    except:
        print 'Invalid Entry'


print 'Maximum is %d' % maximum
print 'Minimum is %d' % minimum

Answer 1

Your problem is that your are checking if (some number) <= None You cannot compare numbers with None . Instead, minimum=float("inf") and maximum=float("-inf") would set minimum to infinity, and maximum to negative infinity. That way, the first number entered would be less than infinity, setting it to minimum , and greater than negative infinity (setting it to maximum ). Note that elif maximum >= num would need to be changed to if maximum >= num (to handle the first entered number).

Answer 2

import sys
maximum = None
minimum = sys.maxsize
while True:
    try:
        num2 = raw_input('Type here ')
        if num2 == 'done':break
        else:
            num = int(num2)
            minimum = min(minimum, num)
            maximum = max(maximum, num)
    except:
        print 'Invalid Entry'


if maximum is None:
    minimum = None

print 'Maximum is %d' % maximum
print 'Minimum is %d' % minimum

Answer 3

You are comparing None and int , Python does not know how to do that. Instead, you should do:

maximum = float('-inf')
minimum = float('inf')

Any int would be greater than -infinity and lower than infinity , so things will work fine. Same thing can not be said about zeroes, so don't use those.

Also, look up min and max builtins .