tailf

tail -f functionality for your python code. Track file appends and truncations.

Python3.6+ is supported.

Examples

pip install tailf==0.2.5

import tailf
import time

with tailf.Tail(filename) as tail:
    while True:
        for event in tail:
            if isinstance(event, bytes):
                print(event.decode("utf-8"), end='')
            elif event is tailf.Truncated:
                print("File was truncated")
            else:
                assert False, "unreachable" # currently. more events may be introduced later
        time.sleep(0.01) # save CPU cycles

# this example requires python3.7
import asyncio
import tailf

async def main():
    with tailf.Tail(filename) as tail:
        while True:
            event = await tail.wait_event()
            if isinstance(event, bytes):
                print(event.decode("utf-8"), end='')
            elif event is tailf.Truncated:
                print("File was truncated")
            else:
                assert False, "unreachable" # currently. more events may be introduced later

asyncio.run(main())

Limitations

• Truncation detection is unreliable in general. It is primarily tracked by file size decrease, which sometimes can be unreliable. In cases when a file grows large and is truncated seldom, this is sufficient.

• Asynchronous tracking is done at timer events (0.01 seconds currently). Inotify support could solve this issue on linux. Feel free to suggest other solutions.