Python - 非空行后的 Readline Control-D 为什么不起作用？

Question

I am new to python, and I am sorry if what I am asking seems odd. I want to loop over each line on standard input and return a modified line to standard output immediately. I have code that works, mostly. However I do not know how to make this work completely.

I have the following code

while True:
    line = sys.stdin.readline()

    if not line:
        break

    sys.stdout.write(line)

When being used interactively this will exit if there is an EOF on a new line, however if there is text before I type Control-D I must give the code twice before it will exit the line, and then once more before the loop will exit.

How do I fix this.

Answer 1

I think my answer from here can be copied immediately:

It has to do with ^D really does: it just stops the current read(2) call.

If the program does int rdbytes = read(fd, buffer, sizeof buffer); and you press ^D inbetween, read() returns with the currently read bytes in the buffer, returning their number. The same happens on line termination; the \n at the end is always delivered.

So only a ^D at the start of a line or after another ^D has the desired effect of having read() return 0 , signalizing EOF.

And this behaviour, of course, affects Python code as well.

Answer 2

A strategy suggested in the python docs is:

for line in sys.stdin:
    sys.stdout.write(line)

See the IO Tutorial .