An empty directory in site-packages is a valid Python module, unfortunately, because
of namespaces. If installing packages in parallel, the pythran module might "exist"
but be empty (hence no __version__ attribute). Catch AttributeError to avoid a narrow
race.

See https://bugs.gentoo.org/902713.

This might still be a Portage issue if there's a substantial delay between creating
the directory and installing the remaining files though.
--- a/Cython/Compiler/Pythran.py
+++ b/Cython/Compiler/Pythran.py
@@ -10,7 +10,7 @@ try:
     import pythran
     pythran_is_pre_0_9 = tuple(map(int, pythran.__version__.split('.')[0:2])) < (0, 9)
     pythran_is_pre_0_9_6 = tuple(map(int, pythran.__version__.split('.')[0:3])) < (0, 9, 6)
-except ImportError:
+except (AttributeError, ImportError):
     pythran = None
     pythran_is_pre_0_9 = True
     pythran_is_pre_0_9_6 = True