def strip(self):
start, end = <NUM_LIT:0>, len(self)<EOL>while start < end and not self.lines[start].strip():<EOL><INDENT>start += <NUM_LIT:1><EOL><DEDENT>while end > start and not self.lines[end - <NUM_LIT:1>].strip():<EOL><INDENT>end -= <NUM_LIT:1><EOL><DEDENT>source = Source()<EOL>source.lines[:] = self.lines[start:end]<EOL>return source<EOL>
return new source object with trailing
            and leading blank lines removed.