This community-built FAQ covers the “Blockchain Summary” exercise from the lesson “Build your own Mini-Blockchain!”.
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This exercise can be found in the following Codecademy content:
Introduction to Blockchain
FAQs on the exercise Blockchain Summary
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I have a few questions regarding the Blockchain class in the exercise:
- What is the use of the attribute
all_transactions in the Blockchain class? In the class, the value of all_transactions was never changed and remains as empty list.
- How to use the
proof_of_work method? Should there be a method for miners to find the nonce for the proof, broadcast it and then waiting for 51% of the participants to verify the proof before a new block is being added to the chain in add_block method?
2 Likes
In this lesson an object-oriented approach is used (i.e. blockchain, block as classes with methods). In the real world is this necessary, or do developers also use functional programming to deal with the same sequences (i.e. hashing, adding blocks, validating, etc.)?
(#3 on the very last step)
I thought this step was supposed to demonstrate something about checking for invalid data after a block has been modified 
Should this still print True after changing block_two_transactions to fake_transactions?
from blockchain import Blockchain
block_one_transactions = {"sender":"Alice", "receiver": "Bob", "amount":"50"}
block_two_transactions = {"sender": "Bob", "receiver":"Cole", "amount":"25"}
block_three_transactions = {"sender":"Alice", "receiver":"Cole", "amount":"35"}
fake_transactions = {"sender": "Bob", "receiver":"Cole, Alice", "amount":"25"}
local_blockchain = Blockchain()
local_blockchain.add_block(block_one_transactions)
local_blockchain.add_block(fake_transactions)
local_blockchain.add_block(block_three_transactions)
print(local_blockchain.validate_chain())
can you find any answer about proof_of_work
ok, I solved it.
I just made 2 diffirence;
1)in blockchain/add_block:
new_block.generate_hash()
# proof = proof_of_work(block)
delete that and made it:
new_block.hash = self.proof_of_work(new_block)
with that way,we send the new_block to the proof_of_work method and it will return us a true hash value(00…)
and we assignment that true hash value to the new_block.hash
2)in block/print_contents:
print(“current hash:”, self.generate_hash()) ----> print(“current hash:”, self.hash)
if you dont do that , when you used print_contents every time you will take a diffirent hash values so our true hash (from add_block) will change and give us another hash value we dont want that.
this way, you can use the proof_of_work method
