# These dependencies are installed using:
#
#   pip install --upgrade
#   pip install --upgrade --no-deps --target vendor/
#
# Vendored dependencies are installed both in the virtual
# environment as well as in the vendor/ directory. This way:
#
# 1. All transitive dependencies of a package are installed in
#    the virtualenv (in the first installation step)
# 2. If there is a binary version of the package available, it
#    will be installed into the virtualenv
# 3. In the third step only (--no-deps) the source version of
#    the (--no-binary) package is installed to vendor/
#
# This allows us to:
#
# 1. Enable mypy to check modules of multiple packages.
# 2. Easily navigate to the source of a vendored dependency
# 3. Use binary versions packages instead of source versions of
#    packages, simply by not including the vendor/ directory in
#    the PYTHONPATH. The version from the virtualenv will then
#    be loaded instead.