Strict use of type annotations has to be a team decision, yes. Checking for them can be integrated into a CI build, though. The typing spec provides for supple

Strict use of type annotations has to be a team decision, yes. Checking for them can be integrated into a CI build, though. The typing spec provides for supplementary "stub files" that can be provided for third-party dependencies without their own annotations. The typeshed project provides these for a fair and quickly increasing number of common dependencies, and is plugged into pycharm and mypy by default: https://github.com/python/typeshed https://github.com/python/typeshed