A Python interface to sendfile(2) syscall.

sendfile(2) is a system call which provides a "zero-copy" way of copying data
from one file descriptor to another (a socket). 

The phrase "zero-copy" refers to the fact that all of the copying of data 
between the two descriptors is done entirely by the kernel, with no 
copying of data into userspace buffers. This is particularly useful 
when sending a file over a socket (e.g. FTP).
