You can achieve same result in Tensorflow using not_equal and where methods.
zero = tf.constant(0, dtype=tf.float32)
where = tf.not_equal(A, zero)
where is a tensor of the same shape as A holding True or False, in the following case
[[True, False],
[False, True]]
This would be sufficient to select zero or non-zero elements from A. If you want to obtain indices you can use wheremethod as follows:
indices = tf.where(where)
where tensor has two True values so indices tensor will have two entries. where tensor has rank of two, so entries will have two indices:
[[0, 0],
[1, 1]]