Message1578

that code should be written as:

xml = ''.join(lines)

this is  quality implementation issue. CPython uses ref counting based optimisations to avoid the quadratic perfomance,
is nevertheless the case that the ''.join idiom is the right way to concatenate many strings that works across Python implementations.

Given that Jython doesn't uses ref counting is unlikely that somethigng reasonably simple can be done to change this.

Java simple switching to use StringBuilder is possible because types are known at compile time.