code: def get_base_branch():
      if not os.path.exists(os.path.join(SRCDIR, ".git")):
          # Not a git checkout, so there's no base branch
          return None
      upstream_remote = get_git_upstream_remote()
      version = sys.version_info
      if version.releaselevel == "alpha":
          base_branch = get_git_remote_default_branch(upstream_remote)
      else:
          base_branch = "{0.major}.{0.minor}".format(version)
      this_branch = get_git_branch()
      if this_branch is None or this_branch == base_branch:
          # Not on a git PR branch, so there's no base branch
          return None
      return upstream_remote + "/" + base_branch
  
imports: import re
  import sys
  import shutil
  import os.path
  import subprocess
  import sysconfig
  import reindent
  import untabify
label_desc: Use image node_id 7 for calling a global function with example usage: get_base_branch() and returns: unknown, None, None