FastIO output gets truncated in windows terminal

Python Version: Python 3.7.7

Describe the bug Output gets truncated when printing a large amount of data over stdout (no problem with file I/O).

To Reproduce Copy FastIO.py from this repo to local, append these lines to the end of the file:

for x in range(5000):
    print(f"{x:0>7} Hello world!")

Expected behaviour It should print from 0000000 Hello world! to 0004999 Hello world!.

Additional context I change the lines above to this:

for x in range(5000):
    print(f"{x:0>7} Hello world!")
    if x % 1000 == 0:  # ofcoz, 1000 doesn't always work
        print(flush=True)

It works fine. This is error-prone. So I would like to ask whether it is possible to flush the output automatically whenever needed?

Thanks in advanced.

[bjorn-martinsson]

If I write like this:

sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(open("test.txt", "w"))

it gives an error:

The reason why this fails is a stupid quirk with this specific implementation of FastIO. The problem is that since the file object is not stored anywhere, it gets garbage collected and is automatically closed. I told @cheran-senthil about this issue back when FastIO was added to pyrival, but he didn’t bother fixing it/ didn’t think it mattered. The fix is easy, just store the file object somewhere

    def __init__(self, file):
        self._file = file
        self._fd = file.fileno()

[jaredliw]

If I write like this:

sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(open("test.txt", "w"))

it gives an error:

Exception ignored in: <__main__.IOWrapper object at 0x00000165229EBBC8>
Traceback (most recent call last):
  File "test.py", line 41, in flush
    write(self._fd, self.buffer.getvalue())
OSError: [Errno 9] Bad file descriptor

is it as expected?