def get_username(prompt="Enter username: ", defaultUser=None):
    user = raw_input(prompt)
    while not len(user):
        if defaultUser:
            user = defaultUser
        else:
            user = raw_input("  You must enter a username: ")
    return user
Get the gradients of the posterior distribution of X in its specific form.
dataset/ETHPy150Open ryran/ravshello/rav-notify.py/get_username--crossover with--dataset/ETHPy150Open SheffieldML/GPy/GPy/models/bayesian_gplvm.py/BayesianGPLVM.get_X_gradients