How Merkle Tree obtain root node hash (example from 'Understanding the ethereum trie')?

Question

I read Understanding the ethereum trie and try to do examples from that article. Now i am at ex1.py - first exaple. Look at code from that example:

import sys
sys.path.append('src')
import trie, utils, rlp

#initialize trie
state = trie.Trie('triedb', trie.BLANK_ROOT)
state.update('\x01\x01\x02', rlp.encode(['hello']))
print 'root hash', state.root_hash.encode('hex')
k, v = state.root_node
print 'root node:', [k, v]
print 'hp encoded key, in hex:', k.encode('hex')

after work around line:

state.update('\x01\x01\x02', rlp.encode(['hello']))

I saw how code create state.root_hash, in example it is:

15da97c42b7ed2e1c0c8dab6a6d7e3d9dc0a75580bbc4f1f29c33996d1415dcc

I obtain another, but not understood how get it. Can anyone explain me?

So we has:

key = pack_nibbles(with_terminator('\x01\x01\x02')
value = rlp.encode(['hello'])

How from that we got state.root_hash?

Answer 1

I read code bad: when we got

key = pack_nibbles(with_terminator('\x01\x01\x02')
value = rlp.encode(['hello'])

which is tantamount to:

key = '\x01\x01\x02'
value = '\xc6\x85hello'

this value stored like [key, value] pair in root_node. Then we get common RLP of root_node (e.g. rlp(['\x01\x01\x02', \xc6\x85hello'])). and obtain key for new entry line in LevelDB, under key = sha3 of that new value:

// one line in DB with
key:   '̈́ �ƅhello
value: 'J[�Q�H+�� ���^�$q�b�����*{'

which is tantamount to:

key:   [' \x01\x01\x02', '\xc6\x85hello']
value: '4a5b19d151e796482b08a1e020f1f7ef5ea7240c0171fd629598fee612892a7b'

This values we got in trie.py, line 151, func get_root_hash:

def get_root_hash(self):
    #...
    val = rlp.encode(self.root_node)
    key = utils.sha3(val)
    self.db.put(key, val)
    return key

so we got state.root_hash