# Pretend x came from somewhere useful.
x = tf.Variable(0)
A = tf.Variable([1, 2, 3])
# Replace the 2 with whatever's in x
A = tf.scatter_update(A, 1, x)

# Pretend x came from somewhere useful.
x = tf.Variable(0)
A = tf.Variable(np.random.rand(3, 3, 3, 3)
# What's the equivalent of A[1, 1, 1, 1] = x ?