Python has a complicated mechanism of checking an objects truthity.
This involves a number of steps, which end with calling two private
methods on an object (if they are implemented). In Python 2 these
two methods are `__nonzero__` and `__len__`, and in Python 3 they
are `__bool__` and `__len__`. Because we *also* define a __len__
method for certain iterable types, this was triggering a situation
in Python 3 where `__nonzero__` wasn't defined, so it was calling
`__len__`, which was returning 0 (for example an SBDebugger with
no targets), and as a result the truthosity was determined to be
False.
We fix this by correctly using ` __bool__` for Python 3, and leave
the behavior under Python 2 unchanged.
Note that this fix is only implemented in the SWIG generation
python script, and not the SWIG generation shell script. Someone
more familiar than me with shell scripts will need to fix them
to support this for Python 3 if desired.
llvm-svn: 252382
