import tensorflow as tf

x1 = tf.constant(1.)
x2 = tf.constant(2.)

with tf.GradientTape(persistent=True) as tape:
    tape.watch(x2)
    y1 = x1 ** 2
    y2 = x2 ** 2

dydx1 = tape.gradient(y1, x1)
dydx2 = tape.gradient(y2, x2)

del tape

f"{dydx1}, {dydx2}"

None, 4.0