为什么它的工作方式不同，即使它在 python 尝试中几乎相同的代码除外？

Question

The question I want to solve is to input two numbers and output the sum until the user finishes.(until the user inputs ctrl+d) Of course, I can solve the problem using sys.stdin, but I want to solve it using while. The two codes below are my codes, the first one works well, but the second one doesn't work well. I don't know the difference between two codes. If anybody knows about the reason, please explain why..

from sys import stdin 
# in this code, when I input ctrl d, program is finished
    try:
        while True:
            a,b = map(int, stdin.readline().split())
            print(a+b)
    except:
        exit()

from sys import stdin 
# in this code, when I input ctrl d, 0 is printed out
    try:
        while 1:
            print(sum(map(int, stdin.readline().split())))
    except:
        exit()

Answer 1

readline() doesn't fail at EOF; it just returns an empty string. Splitting an empty string is fine. map ping int across an empty list is fine. Summing an empty iterable is fine (and results in zero).

In the first version, it’s the a, b unpacking that fails, but there's no way to tell the difference when you throw away all the exception information and catch an overly broad class of exceptions at the same time.

Never use except ; use except Exception to avoid catching low-level flow control exceptions. And if you feel the need to catch an exception you will otherwise ignore, consider logging the fact that you caught it for debugging purposes.

If you want to use sys.stdin , a for loop is better ( line will continue to end with \n ):

for line in stdin:
    print(sum(map(int, line.split())))

If you want to use a while loop, input is better:

while True:
    try:
        line = input()
    except EOFError:
        break

    print(sum(map(int, line.split())))