Python 写入缓冲区而不是文件

Question

I'm pretty new to a Python, but I've faced a weird behavior that I can't explain/solve. Basically, I need to forward python script output to a file.

Example:

while True:
  print('tick')
  time.sleep(5)

then redirect output to the file

python test.py >> test.log 2>&1

But the thing is the file is empty until the script is finished. Looks like it writes the output to some buffer and only at the end sends this buffer to a file.

This is totally unacceptable for me, as I have a script that is running 24/7 and in this case, I will never get proper logs. I need real-time writing to a file.

I know it might be fixed using

with open('test.log', mode='a') as log_file:

But in this case, I will lose the ability to view the result in the terminal. Besides that, I will be strictly limited to a file specified inside of a script.

I suppose it is not actually Python issue, but more generic. Still, is that possible to do instant writing to a file, just like I see it in the terminal?

Answer 1

Looks like it writes the output to some buffer

That's correct. You can disable this with flush=True , so:

while True:
  print('tick', flush=True)
  time.sleep(5)

Answer 2

Try this:

with open('log.log', 'w+') as log_file:    
print('tick', file=log_file)

In that way the print output will go to file instead stdout