python-sendfile 2.0.0-6ubuntu2 (amd64 binary) in ubuntu xenial

 Python library 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).