This question should be related to:
But I am wondering how to do that through pygit2?
From PyGit Documentation
Either of these should work
#!/usr/bin/python
from pygit2 import Repository
repo = Repository('/path/to/your/git/repo')
# option 1
head = repo.head
print("Head is " + head.name)
# option 2
head = repo.lookup_reference('HEAD').resolve()
print("Head is " + head.name)
You'll get the full name including /refs/heads/. If you don't want that strip it out or use shorthand instead of name.
./pygit_test.py
Head is refs/heads/master
Head is refs/heads/master