$ ~/workspace/pre-commit/venv/bin/pre-commit install -t post-checkout
pre-commit installed at .git/hooks/post-checkout
$ git add .
$ git commit -m 'add config'
[master (root-commit) d15280a] add config
 1 file changed, 5 insertions(+)
 create mode 100644 .pre-commit-config.yaml
$ git status
On branch master
nothing to commit, working tree clean
$ git status
On branch master
nothing to commit, working tree clean
$ git checkout master -b wat
Switched to a new branch 'wat'
identity.............................................(no files to check)Skipped
- hook id: identity
$ touch foo.py
$ git status
On branch wat
Untracked files:
	foo.py

nothing added to commit but untracked files present
$ git add .
$ git commit -m "add foo"
[wat 1ca3ef0] add foo
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 foo.py
$ git checkout master 
Switched to branch 'master'
identity.............................................(no files to check)Skipped
- hook id: identity
$ git checkout wat
Switched to branch 'wat'
identity.................................................................Passed
- hook id: identity
- duration: 0.04s

foo.py

$ cat .pre-commit-config.yaml 
repos:
-   repo: meta
    hooks:
    -   id: identity
        stages: [post-checkout]