python git checkout using pygit2

checkout.py

import pygit2


def checkout_branch(path, branch_name):
    repo = pygit2.Repository(path)

    # If the branch isn't already in the local list, 
    # you have to create a ref for it to point at 
    # in order to avoid detached head state
    if branch_name not in repo.branches.local:
        print(f"Branch {branch_name} not found in local branches")
        remote_branch = "origin/" + branch_name
        if remote_branch not in repo.branches.remote:
            raise SystemExit(f"Branch {remote_branch} not found in remote branches")
        (commit, remote_ref) = repo.resolve_refish(remote_branch)
        repo.create_reference("refs/heads/" + branch_name, commit.hex)

    branch = repo.lookup_branch(branch_name)
    print(f"Branch name: {branch.name}")

    repo.checkout(branch)
    print(f"Is branch head? {branch.is_head()}")

    (commit, branch_remote) = repo.resolve_refish("origin/" + branch_name)
    print(f"Remote branch: {branch_remote.name}")
    branch.upstream = branch_remote


checkout_branch("path/to/your/repo", "branch-name")

# This avoids detached head and also sets the remote target correctly