#18125 Multiple Python versions for different modules within a single monolithic repo Issue created by ericsun2 Is your feature request related to a problem? Please describe. In a monorepo, there are many different services/modules, it is quite useful to be able to use different Python version to build a certain module.

monorepo/
        .python-version
        service_foo/
                   .python-version
                   src/python/...
        service_bar
        library_xyz
        library_baz/
                   .python-version

For example, with Python 3.7 reaches its EOL, we have to upgrade, but not every team in the monorepo will be ready at the same pace. We have to compile

library_baz

and

service_bar

with Python 3.9 first, and push the 3.9-based artifact to internal pypi. Describe the solution you'd like Allow the

.python-version

to be used to override the Python version at sub module level. If

library_baz

is used by both

service_foo

and

service_bar

yet these 2 services are not upgraded to the new Python at the same time, it might still be a problem, therefore if

service_foo

has Python 3.9 specified then it will also use 3.9 to build its dependencies including

library_baz

even if

library_baz

is still pinned to 3.7 Once all the services & modules in the monorepo have migrated to 3.9, it will be easy to clean up the

.python-version

file at sub module level. Describe alternatives you've considered The other alternative is to use multiple git branches, each one is associated with a specific Python version. Everything (services, modules) in that branch will use the same Python version, and the branch tag will be used to publish artifact. Yet the artifact publish process can be hard to manage in this case. Additional context If there's any best practice and/or advice how to handle major Python version upgrade in a monorepo scenario, that will be great. pantsbuild/pants