def code_verifier(n_bytes=64):
 verifier = base64.urlsafe_b64encode(os.urandom(n_bytes)).rstrip('=')
 if (len(verifier) < 43):
  raise ValueError('Verifier too short. n_bytes must be > 30.')
 elif (len(verifier) > 128):
  raise ValueError('Verifier too long. n_bytes must be < 97.')
 else:
  return verifier

def code_verifier ( n_bytes = 64 ) : verifier = base64 . urlsafe_b64encode ( os . urandom ( n_bytes ) ) . rstrip ( '=' ) if ( len ( verifier ) < 43 ) : raise ValueError ( 'Verifier too short. n_bytes must be > 30.' ) elif ( len ( verifier ) > 128 ) : raise ValueError ( 'Verifier too long. n_bytes must be < 97.' ) else : return verifier
generates a code_verifier as described in section 4 .