def git_version():
  import subprocess
  cmd = ['git', 'describe', '--always', '--match', 'v[0-9].*', '--dirty']
  p = subprocess.Popen(cmd, stdout = subprocess.PIPE)
  v = p.communicate()[0].strip()
  r = p.returncode
  if r != 0:
    raise subprocess.CalledProcessError(r, ' '.join(cmd))
  return v