Lock part of a file based on file descriptor fd from the C
runtime. Raises IOError on failure. The locked region
of the file extends from the current file position for nbytes
bytes, and may continue beyond the end of the file. mode must
be one of the LK_* constants listed below.
Multiple regions in a file may be locked at the same time, but may
not overlap. Adjacent regions are not merged; they must be unlocked
Create a C runtime file descriptor from the file handle
handle. The flags parameter should be a bit-wise OR of
os.O_APPEND, os.O_RDONLY, and
os.O_TEXT. The returned file descriptor may be used as a
parameter to os.fdopen() to create a file object.