docs: def fingerprint_from_var(var):
      """Extract a fingerprint from a GPG public key"""
      vsn = gpg_version()
      cmd = flatten([gnupg_bin(), gnupg_home()])
      if vsn[0] >= 2 and vsn[1] < 1:
          cmd.append("--with-fingerprint")
  
      output = polite_string(stderr_with_input(cmd, var)).split('\n')
      if not output[0].startswith('pub'):
          raise CryptoritoError('probably an invalid gpg key')
  
      if vsn[0] >= 2 and vsn[1] < 1:
          return output[1] \
              .split('=')[1] \
              .replace(' ', '')
  
      return output[1].strip()