In Python versions older than 3.2 hasattr is not robust as it masks real
errors. And usually is not efficient as a call to hasattr is often
followed by another call to getattr. It is best to avoid using it
completely.
See https://docs.python.org/3/whatsnew/3.2.html#other-language-changes
These are only needed in C code. With Python files the signatures are
automatically generated. The only drawback is the return value is not
included in the signature, so document it in the body of the docstring.
We need to keep hold of the strings which we create. We must also hold
on to the array of strings which we assing to our git_strarray.
We were not doing the latter, which meant that our strings may have been
freed too early, leaving us with with memory access errors (though often
not leading to a crash due to the custom allocator in python).
As we need to keep hold of two/three pieces of information, this looks
like a good place to introduce a context manager. This allows us to
keep these pointers alive without burdening the call sites with a return
of multiple objects they have no use for.
