There is an open bug about this on the MapProxy issue tracker here: https://github.com/mapproxy/mapproxy/issues/279

Judging from the comments here and on the issue tracker the most reliable way to get it working again is to downgrade from Python 2.7.12 to 2.7.9.

You are using virtualenv, you can install Python 2.7.9 alongside 2.7.12 (uncheck "Add to PATH" during installation to keep 2.7.12 the default) and then create an environment with 2.7.9:

C:\code>virtualenv --python=C:\Python279\python.exe mapproxy_venv
C:\code>mapproxy_venv\Scripts\activate
(mapproxy_venv) C:\code>python --version
Python 2.7.9

And then continue with the rest of the installation.

Update, Jan 2017:

There is a new [MapProxy] 1.9.1 release which should fix this.

Source: https://github.com/mapproxy/mapproxy/issues/279

Judging from the comments here and on the issue tracker the most reliable way to get it working again is to downgrade from Python 2.7.12 to 2.7.9.

You are using virtualenv, you can install Python 2.7.9 alongside 2.7.12 (uncheck "Add to PATH" during installation to keep 2.7.12 the default) and then create an environment with 2.7.9:

C:\code>virtualenv --python=C:\Python279\python.exe mapproxy_venv
C:\code>mapproxy_venv\Scripts\activate
(mapproxy_venv) C:\code>python --version
Python 2.7.9

And then continue with the rest of the installation.