VC features

Rule of thumb

if it's a shared library that something other than Python will use, you only need python in build to activate features. You need the features block;
if it is a shared library that is tied to a Python API (e.g. Boost Python), you need BOTH, and the features block.
If it is a library that has compiled content, but is used only from Python, you need Python in both build and runtime requirements, but you do NOT need the features block.

To providing features add the following lines to the build section.

build:
    features:
        - vc9   # [win and py27]
        - vc10  # [win and py34]
        - vc14  # [win and py35]

Also, add a python dependency to the build requirements (unless it is already a requirement like NumPy for instance).

requirements:
    build:
        - python  # [win]

Often it is required to add a python dependency to the test requirements. This is how you do this.

test:
    requires:
        - python 2.7.*  # [win and py27]
        - python 3.4.*  # [win and py34]
        - python 3.5.*  # [win and py35]