AppVeyor updates to Python version may be newer than the available PyPI wheels available. Since Python library wheels are often not immediately available for recently-released Python versions, this can lead to CI test nuisance errors at setup. Projects can experience CI errors on Numpy setup as AppVeyor attempts to compile Numpy since the wheel doesn’t exist yet for pre-release Python versions.

AppVeyor has several Python versions installed. The AppVeyor Python version selection method is OS-dependent. The examples are shown specific to Windows and Linux for didactic clarity. They would normally be merged to a single .appveyor.yml.

Select Python version on AppVeyor Windows CI by setting .appveyor.yml to the desired AppVeyor Windows Python version directory:

environment:
  PY_DIR: C:/Python<version desired>

init:
- cmd: set PATH=%PY_DIR%;%PY_DIR%\Scripts;%PATH%

Select Python version on AppVeyor Linux CI can use “stack: python 3” or set .appveyor.yml to the desired AppVeyor Linux Python version directory: