code: def read(self, offset, length):
          
          readfile = getattr(self, 'readfile', None)
          if readfile is None:
              return SFTP_OP_UNSUPPORTED
          try:
              if self.__tell is None:
                  self.__tell = readfile.tell()
              if offset != self.__tell:
                  readfile.seek(offset)
                  self.__tell = offset
              data = readfile.read(length)
          except IOError, e:
              self.__tell = None
              return SFTPServer.convert_errno(e.errno)
          self.__tell += len(data)
          return data
docs: Read up to C{length} bytes from this file, starting at position
          C{offset}.  The offset may be a python long, since SFTP allows it
          to be 64 bits.
  
          If the end of the file has been reached, this method may return an
          empty string to signify EOF, or it may also return L{SFTP_EOF}.
  
          The default implementation checks for an attribute on C{self} named
          C{readfile}, and if present, performs the read operation on the python
          file-like object found there.  (This is meant as a time saver for the
          common case where you are wrapping a python file object.)
  
          @param offset: position in the file to start reading from.
          @type offset: int or long
          @param length: number of bytes to attempt to read.
          @type length: int
          @return: data read from the file, or an SFTP error code.
          @rtype: str