def valid_chain(chain):
'''
Determine if a given blockchain is valid by looping through
each block and verifying both hash and the proof
:param chain: <list> A blockchain to verify
:return: <bool> True if valid, else False
'''
last_block = chain[0]
current_index = 1
while current_index < len(chain):
block = chain[current_index]
print(f'{last_block}')
print(f'{block}')
print('\n-------\n')
# Check of the current block is correct
if block['previous_hash'] != Hash.hash(last_block):
return False
# Check that the proof of work is correct
# by validating the last blocks proof against the current blocks proof
if not Proof.valid_proof(last_block['proof'], block['proof']):
return False
last_block = block
current_index += 1
# If all above checks pass, then the block is valid.
return True
def test_valid_proof(self):
'''
Ensures that the validation method is working correctly.
'''
self.assertTrue(Proof.valid_proof(1, 72608))
