2 daemons write to a single file /w python file IO

[Andrey]

HI

i have a newbie question about the file() function.
I have 2 daemons running on my linux box.

1 will record the IDs to a file - logs.txt
other 1 will open this file, read the IDs, and then "Clean up the 
file" -logs.txt

Since these 2 daemons will run every 2-5mins, I think this will crash, isn't 
it? When both daemons try to write to the file at the same time.

I am wondering if this won't crash, OR if there is some simple high-level 
functions can lock the file while writing...
I also wonder if one side locked the file, what happens if the other side 
try to open this locked file? raise error? so i also need to write a loop to 
wait for the file to release locking?

seems a basic easy thing but i just cannot find an simple answer.
I always advoid this issue by putting them in mysql (well, fast and hassle 
free for locking)

Thanks
Jay