my_list = [0.3, 0.5, 0.79, 0.2, 0.11]
m = max(my_list)

[0 if i != m else i for i in my_list]

[0, 0, 0.79, 0, 0]

a_max = tf.where(tf.equal(a, tf.reduce_max(a)), a, tf.zeros_like(a))