Walking the tangle—How to get the parents?

Question

Looking at Pseudocode to walk the tangle?, in order to walk the tangle you look at the open tips and then you look for the parents. getTips gives you a list of all the open tips. What API call is needed however to get the parents?

Answer 1

The 2 parents of a transactions are called trunk transaction and branch transaction.

You get them like this: (It's python but the names and arguments in other libraries are very similar)

getTips returns a list of transaction hashes

tips = api.get_tips()['hashes']

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Call getTrytes to fetch a transaction from its hash. (tips[0] for the first transaction in tips)

transaction_trytes = api.get_trytes([tips[0]])['trytes']

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Transaction.from_tryte_string takes the trytes and casts them into a Transaction-object

transaction = Transaction.from_tryte_string(transaction_trytes[0])

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To get the parents, use the properties of the transaction

trunkTransactionHash = transaction.trunk_transaction_hash()
branchTransactionHash = transaction.branch_transaction_hash()

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Then you can call getTrytes again

trunkTransaction = api.get_trytes([trunkTransactionHash])