pypi currently contains the following versions:
1.4, 1.5, 1.6, 1.9.0, 1.9.3, 1.9.4, 1.62, 1.63, 1.65, 1.67, 1.78, 1.79, 1.80, 1.81
As you can see by the order, version 1.81 is considered the newest, even though 1.9.4 is actually newer. This makes it hard to set up version ranges for pip.