I tried on trusty and is also picked numpy-1.11.0-cp27-cp27mu-manylinux1_x86_64.whl using the system python 2.7 (in a virtualenv with pip 8.1.1):
import pip pip.pep425tags.get_abi_tag() 'cp27mu'
Outside of the virtualenv I still have the pip version from ubuntu trusty and it does cannot detect ABI tags: $ /usr/bin/pip --version pip 1.5.4 from /usr/lib/python2.7/dist-packages (python 2.7)
import pip pip.pep425tags.get_abi_tag() Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'module' object has no attribute 'get_abi_tag'
But we don't really care because manylinux1 wheels can only be installed by pip 8.1 and later. Previous versions of pip should just ignore those wheels and try to install from the source tarball instead. -- Olivier