def maskRegion(self, region):
if region.start < <NUM_LIT:0> or region.end < <NUM_LIT:0> orregion.start > len(self) or region.end > len(self):<EOL><INDENT>raise SequenceError("<STR_LIT>" + str(region.start) + "<STR_LIT>" +<EOL>str(region.end) + "<STR_LIT>" + self.name + "<STR_LIT>" +<EOL>"<STR_LIT>" +<EOL>"<STR_LIT>" +<EOL>str(len(self)))<EOL><DEDENT>if self.mutableString:<EOL><INDENT>for i in range(region.start, region.end + <NUM_LIT:1>):<EOL><INDENT>self.sequenceData[i] = '<STR_LIT:N>'<EOL><DEDENT><DEDENT>else:<EOL><INDENT>self.sequenceData = "<STR_LIT>".join([self.sequenceData[:region.start],<EOL>("<STR_LIT:N>" * (region.end - region.start + <NUM_LIT:1>)),<EOL>self.sequenceData[region.end + <NUM_LIT:1>:]])<EOL><DEDENT>
Replace nucleotides in this sequence in the regions given by Ns

:param region: any object with .start and .end attributes. Co-ords are
               zero based and inclusive of both end points. Any other
               attributes (e.g. chrom.) are ignored.
:raise SequenceError: if region specifies nucleotides not present in
                      this sequence