Parallel(?) programming with python

[Andreas Croci]

tI would like to write a program, that reads from the network a fixed 
amount of bytes and appends them to a list. This should happen once a 
second.

Another part of the program should take the list, as it has been filled 
so far, every 6 hours or so, and do some computations on the data (a FFT).

Every so often (say once a week) the list should be saved to a file, 
shorthened in the front by so many items, and filled further with the 
data coming fom the network. After the first saving of the whole list, 
only the new part (the data that have come since the last saving) should 
be appended to the file. A timestamp is in the data, so it's easy to say 
what is new and what was already there.

I'm not sure how to do this properly: can I write a part of a program 
that keeps doing its job (appending data to the list once every second) 
while another part computes something on the data of the same list, 
ignoring the new data being written?

Basically the question boils down to wether it is possible to have parts 
of a program (could be functions) that keep doing their job while other 
parts do something else on the same data, and what is the best way to do 
this.