In the function update_parameters(), the comment indicates using copy.deepcopy(…) for W1 and W2. My question is why not for b1 and b2?
Thank you in advance.
Hello @hungng777,
Actually, it is fine to have or not have deepcopy for any of the Ws and bs there. I tested it, and I suggest you to do the same. 
Usually, we use deepcopy to avoid modifying the original copy, but here in this exercise, that is not a problem because, if you read the code again, the original copy is only used to produce the modified version and then it will get replaced. The original copy is not supposed to be re-used anywhere else.
Cheers,
Raymond
Right, you have to be careful because objects are passed “by reference” in python. That means you may accidentally be modifying the global object. In this assignment it doesn’t matter because they changed the test cases so that they don’t fail if you modify the global objects. When you get to the same point in Week 4, that is not the case, so care is required.
Here’s a thread which discusses what’s going on here in more detail.
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