Python Implementation of the Ethereum Trie structure

This library and repository was previously located at pipermerriam/py-trie. It was transferred to the Ethereum foundation GitHub in November 2017 and renamed to py-trie.

Installation

pip install trie

Development

pip install -e .[dev]

Running the tests

You can run the tests with:

pytest tests

Or you can install tox to run the full test suite.

Releasing

Pandoc is required for transforming the markdown README to the proper format to render correctly on pypi.

For Debian-like systems:

apt install pandoc

Or on OSX:

brew install pandoc

To release a new version:

bumpversion $$VERSION_PART_TO_BUMP$$
git push && git push --tags
make release

How to bumpversion

The version format for this repo is {major}.{minor}.{patch} for stable, and {major}.{minor}.{patch}-{stage}.{devnum} for unstable (stage can be alpha or beta).

To issue the next version in line, use bumpversion and specify which part to bump, like bumpversion minor or bumpversion devnum.

If you are in a beta version, bumpversion stage will switch to a stable.

To issue an unstable version when the current version is stable, specify the new version explicitly, like bumpversion --new-version 4.0.0-alpha.1 devnum

Usage

>>> from trie import HexaryTrie
>>> t = HexaryTrie(db={})
>>> t.root_hash
b'V\xe8\x1f\x17\x1b\xccU\xa6\xff\x83E\xe6\x92\xc0\xf8n[H\xe0\x1b\x99l\xad\xc0\x01b/\xb5\xe3c\xb4!'
>>> t.set(b'my-key', b'some-value')
>>> t.get(b'my-key')
b'some-value'
>>> t.exists(b'another-key')
False
>>> t.set(b'another-key', b'another-value')
>>> t.exists(b'another-key')
True
>>> t.delete(b'another-key')
>>> t.exists(b'another-key')
False

You can also use it like a dictionary.

>>> from trie import HexaryTrie
>>> t = HexaryTrie(db={})
>>> t.root_hash
b'V\xe8\x1f\x17\x1b\xccU\xa6\xff\x83E\xe6\x92\xc0\xf8n[H\xe0\x1b\x99l\xad\xc0\x01b/\xb5\xe3c\xb4!'
>>> t[b'my-key'] = b'some-value'
>>> t[b'my-key']
b'some-value'
>>> b'another-key' in t
False
>>> t[b'another-key']  = b'another-value'
>>> b'another-key' in t
True
>>> del t[b'another-key']
>>> b'another-key' in t
False

Traversing (inspecting trie internals)

>>> from trie import HexaryTrie
>>> t = HexaryTrie(db={})
>>> t.root_hash
b'V\xe8\x1f\x17\x1b\xccU\xa6\xff\x83E\xe6\x92\xc0\xf8n[H\xe0\x1b\x99l\xad\xc0\x01b/\xb5\xe3c\xb4!'
>>> t[b'my-key'] = b'some-value'
>>> t[b'my-other-key']  = b'another-value'

# Look at the root node:
>>> root_node = t.traverse(())
>>> root_node
HexaryTrieNode(sub_segments=((0x6, 0xd, 0x7, 0x9, 0x2, 0xd, 0x6),), value=b'', suffix=(), raw=[b'\x16\xd7\x92\xd6', b'\xb4q\xb8h\xec\x1c\xe1\xf4\\\x88\xda\xb4\xc1\xc2n\xbaw\xd0\x9c\xf1\xacV\xb4Dk\xa7\xe6\xd7qf\xc2\x82'])

# the root node is an extension down, because the first 7 nibbles are the same between the two keys

# Let's walk down to the child of that extension 
>>> prefix6d792d6 = t.traverse(root_node.sub_segments[0])
>>> prefix6d792d6
HexaryTrieNode(sub_segments=((0xb,), (0xf,)), value=b'', suffix=(), raw=[b'', b'', b'', b'', b'', b'', b'', b'', b'', b'', b'', [b' ey', b'some-value'], b'', b'', b'', [b' ther-key', b'another-value'], b''])

# A branch node separates the second nibbles of b'k' and b'o': 0xb and 0xf
# Notice the position of the children in the 11th and 15th index

# Another way to get there without loading the root node from the database is using traverse_from:
>>> assert t.traverse_from(root_node, root_node.sub_segments[0]) == prefix6d792d6

# Embedded nodes can be traversed to the same way as nodes stored in the database:

>>> t.traverse(root_node.sub_segments[0] + (0xb,))
HexaryTrieNode(sub_segments=(), value=b'some-value', suffix=(0x6, 0x5, 0x7, 0x9), raw=[b' ey', b'some-value'])

# This leaf node includes the suffix (the rest of the key, in nibbles, that haven't been traversed,
# just b'ey': 0x6579

Walking a full trie

To walk through the full trie (for example, to verify that all node bodies are present in the database), use HexaryTrieFog and the traversal API above.

For example:

>>> from trie import HexaryTrie
>>> t = HexaryTrie(db={})
>>> t.root_hash
b'V\xe8\x1f\x17\x1b\xccU\xa6\xff\x83E\xe6\x92\xc0\xf8n[H\xe0\x1b\x99l\xad\xc0\x01b/\xb5\xe3c\xb4!'
>>> t[b'my-key'] = b'some-value'
>>> t[b'my-other-key']  = b'another-value'
>>> t[b'your-key'] = b'your-value'
>>> t[b'your-other-key'] = b'your-other-value'
>>> t.root_hash
b'\xf8\xdd\xe4\x0f\xaa\xf4P7\xfa$\xfde>\xec\xb4i\x00N\xa3)\xcf\xef\x80\xc4YU\xe8\xe7\xbf\xa89\xd5'

# Initialize a fog object to track unexplored prefixes in a trie walk
>>> from from trie.fog import HexaryTrieFog
>>> empty_fog = HexaryTrieFog()
# At the beginning, the unexplored prefix is (), which means that none of the trie has been explored
>>> prefix = empty_fog.nearest_unknown()
()

# So we start by exploring the node at prefix () -- which is the root node:
>>> node = t.traverse(prefix)
HexaryTrieNode(sub_segments=((0x6,), (0x7,)), value=b'', suffix=(), raw=[b'', b'', b'', b'', b'', b'', b"\x03\xd2vk\x85\xce\xe1\xa8\xdb'F\x8c\xe5\x15\xc6\n+M:th\xa1\\\xb13\xcc\xe8\xd0\x1d\xa7\xa8U", b"\x1b\x8d'\xb3\x99(yX\xaa\x96C!\xba'X \xbb|\xa6,\xb5V!\xd3\x1a\x05\xe5\xbf\x02\xa3fR", b'', b'', b'', b'', b'', b'', b'', b'', b''])
# and mark the root as explored, while defining the unexplored children:
>>> level1fog = empty_fog.explore(prefix, node.sub_segments)
# Now the unexplored prefixes are the keys starting with the four bits 6 and the four bits 7.
# All other keys are known to not exist (and so have been explored)
>>> level1fog
HexaryTrieFog<SortedSet([(0x6,), (0x7,)])>

# So we continue exploring. The fog helps choose which prefix to explore next:
>>> level1fog.nearest_unknown()
(0x6,)
# We can also look for the nearest unknown key to a particular target
>>> prefix = level1fog.nearest_unknown((8, 1))
(0x7,)
>>> node7 = node.traverse(prefix)
HexaryTrieNode(sub_segments=((0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6),), value=b'', suffix=(), raw=[b'\x00\x96\xf7W"\xd6', b"\xe2\xe2oN\xe1\xf8\xda\xc1\x8c\x03\x92'\x93\x805\xad-\xef\x07_\x0ePV\x1f\xb5/lVZ\xc6\xc1\xf9"])
# We found an extension node, and mark it in the fog
# For simpliticy, we'll start clobbering the `fog` variable
>>> fog = level1fog.explore(prefix, node7.sub_segments)
HexaryTrieFog<SortedSet([(0x6,), (0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6)])>

# Let's explore the next branch node and see what's left
>>> prefix = fog.nearest_unknown((7,))
(0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6)
>>> node796f75722d6 = t.traverse(prefix)
HexaryTrieNode(sub_segments=((0xb,), (0xf,)), value=b'', suffix=(), raw=[b'', b'', b'', b'', b'', b'', b'', b'', b'', b'', b'', [b' ey', b'your-value'], b'', b'', b'', [b' ther-key', b'your-other-value'], b''])
# Notice that the branch node inlines the values, but the fog and annotated node ignore them for now
>>> fog = fog.explore(prefix, node796f75722d6.sub_segments)
HexaryTrieFog<SortedSet([(0x6,), (0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb), (0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xf)])>

# Index keys may not matter for your use case, so you can leave them out, but there's one more
# feature to consider: we can look directionally to the right of an index for the nearest prefix.
>>> prefix = fog.nearest_right((0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xc))
(0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xf)
# That same index key would give a closer prefix to the left if direction didn't matter
>>> fog.nearest_unknown((0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xc))
(0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb)
# So we traverse to this last embedded leaf node at `prefix`
>>> a_leaf_node = t.traverse(prefix)
HexaryTrieNode(sub_segments=(), value=b'your-other-value', suffix=(0x7, 0x4, 0x6, 0x8, 0x6, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb, 0x6, 0x5, 0x7, 0x9), raw=[b' ther-key', b'your-other-value'])
# we mark the prefix as fully explored like so:
>>> fog = fog.explore(prefix, a_leaf_node.sub_segments)
HexaryTrieFog<SortedSet([(0x6,), (0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb)])>
# Notice that sub_segments was empty, and the prefix has disappeared from our list of unexplored prefixes

# So far we have dealt with an un-changing trie, but what if it is
#   modified while we are working on it?
>>> del t[b'your-other-key']
>>> t[b'your-key-rebranched'] = b'your-value'
>>> t.root_hash
b'"\xc0\xcaQ\xa7X\x08E\xb5"A\xde\xbfY\xeb"XY\xb1O\x034=\x04\x06\xa9li\xd8\x92\xadP'

# The unexplored prefixes we have before might not exist anymore. They might:
#   1. have been deleted entirely, in which case, we will get a blank node, and need no special treatment
#   2. lead us into the middle of a leaf or extension node, which makes things tricky
>>> prefix = fog.nearest_unknown((8,))
(0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb)
>>> t.traverse(prefix)
TraversedPartialPath: Could not traverse through HexaryTrieNode(sub_segments=((0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb, 0x6, 0x5, 0x7, 0x9),), value=b'', suffix=(), raw=[b'\x19our-key', b'f\xbe\x88\x8f#\xd5\x15-8\xc0\x1f\xfb\xf7\x8b=\x98\x86 \xec\xdeK\x07\xc8\xbf\xa7\x93\xfa\x9e\xc1\x89@\x00']) at (0x7,)

# Let's drill into what this means:
#   - We fully traversed to a node at prefix (7,)
#   - We tried to traverse into the rest of the prefix
#   - We only got part-way through the extension node
#   - That extension node has a sub-segment of (0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb, 0x6, 0x5, 0x7, 0x9)

# So what do we do about it? Catch the exception, and explore with the fog slightly differently
>>> from trie.exceptions import TraversedPartialPath
>>> last_exception = None
>>> try:
      t.traverse(prefix)
    except TraversedPartialPath as exc:
      last_exception = exc

# We can now drive the exploration of the extension node further, by back-forming sub-segments:
>>> sub_segments = [
      last_exception.nibbles_traversed + segment
      for segment in last_exception.node.sub_segments
]
>>> fog = fog.explore(prefix, sub_segments)
HexaryTrieFog<SortedSet([(0x6,), (0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb, 0x7, 0x9, 0x6, 0xf, 0x7, 0x5, 0x7, 0x2, 0x2, 0xd, 0x6, 0xb, 0x6, 0x5, 0x7, 0x9)])>
# So now we can pick up where we left of, traversing to the child of the extension node, and so on.

.. NOTE: If you are traversing a large trie, note that traverse() re-navigates from the root at each call. You might consider using TrieFrontierCache and HexaryTrie.traverse_from() to minimize database lookups. See the tests in tests/test_hexary_trie_walk.py for some examples.

BinaryTrie

Note: One drawback of Binary Trie is that one key can not be the prefix of another key. For example, if you already set the value value1 with key key1, you can not set another value with key key or key11 and the like.

BinaryTrie branch and witness helper functions

>>> from trie import BinaryTrie
>>> from trie.branches import (
>>>     check_if_branch_exist,
>>>     get_branch,
>>>     if_branch_valid,
>>>     get_witness_for_key_prefix,
>>> )
>>> t = BinaryTrie(db={})
>>> t.root_hash
b"\xc5\xd2F\x01\x86\xf7#<\x92~}\xb2\xdc\xc7\x03\xc0\xe5\x00\xb6S\xca\x82';{\xfa\xd8\x04]\x85\xa4p"
>>> t.set(b'key1', b'value1')
>>> t.set(b'key2', b'value2')

Now Trie looks like this:

    root --->  (kvnode, *common key prefix*)
                         |
                         |
                         |
                    (branchnode)
                     /         \
                    /           \
                   /             \
(kvnode, *remain kepath*)(kvnode, *remain kepath*)
            |                           |
            |                           |
            |                           |
  (leafnode, b'value1')       (leafnode, b'value2')

>>> # check_if_branch_exist function
>>> check_if_branch_exist(t.db, t.root_hash, b'key')
True
>>> check_if_branch_exist(t.db, t.root_hash, b'key1')
True
>>> check_if_branch_exist(t.db, t.root_hash, b'ken')
False
>>> check_if_branch_exist(t.db, t.root_hash, b'key123')
False
>>> # get_branch function
>>> get_branch(t.db, t.root_hash, b'key1')
(b'\x00\x82\x1a\xd9^L|38J\xed\xf31S\xb2\x97A\x8dy\x91RJ\x92\xf5ZC\xb4\x99T&;!\x9f\xa9!\xa2\xfe;', b"\x01*\xaccxH\x89\x08}\x93|\xda\xb9\r\x9b\x82\x8b\xb2Y\xbc\x10\xb9\x88\xf40\xef\xed\x8b'\x13\xbc\xa5\xccYGb\xc2\x8db\x88lPs@)\x86v\xd7B\xf7\xd3X\x93\xc9\xf0\xfd\xae\xe0`j#\x0b\xca;\xf8", b'\x00\x11\x8aEL3\x839E\xbd\xc4G\xd1xj\x0fxWu\xcb\xf6\xf3\xf2\x8e7!M\xca\x1c/\xd7\x7f\xed\xc6', b'\x02value1')

Node started with b'\x00', b'\x01' and b'\x02' are kvnode, branchnode and leafnode respectively.

>>> get_branch(t.db, t.root_hash, b'key')
(b'\x00\x82\x1a\xd9^L|38J\xed\xf31S\xb2\x97A\x8dy\x91RJ\x92\xf5ZC\xb4\x99T&;!\x9f\xa9!\xa2\xfe;',)
>>> get_branch(t.db, t.root_hash, b'key123') # InvalidKeyError
>>> get_branch(t.db, t.root_hash, b'key5') # there is still branch for non-exist key
(b'\x00\x82\x1a\xd9^L|38J\xed\xf31S\xb2\x97A\x8dy\x91RJ\x92\xf5ZC\xb4\x99T&;!\x9f\xa9!\xa2\xfe;',)
>>> # if_branch_valid function
>>> v = t.get(b'key1')
>>> b = get_branch(t.db, t.root_hash, b'key1')
>>> if_branch_valid(b, t.root_hash, b'key1', v)
True
>>> v = t.get(b'key5') # v should be None
>>> b = get_branch(t.db, t.root_hash, b'key5')
>>> if_branch_valid(b, t.root_hash, b'key5', v)
True
>>> v = t.get(b'key1')
>>> b = get_branch(t.db, t.root_hash, b'key2')
>>> if_branch_valid(b, t.root_hash, b'key1', v) # KeyError
>>> if_branch_valid([], t.root_hash, b'key1', v) # AssertionError
>>> # get_witness_for_key_prefix function
>>> get_witness_for_key_prefix(t.db, t.root_hash, b'key1') # equivalent to `get_branch(t.db, t.root_hash, b'key1')`
(b'\x00\x82\x1a\xd9^L|38J\xed\xf31S\xb2\x97A\x8dy\x91RJ\x92\xf5ZC\xb4\x99T&;!\x9f\xa9!\xa2\xfe;', b"\x01*\xaccxH\x89\x08}\x93|\xda\xb9\r\x9b\x82\x8b\xb2Y\xbc\x10\xb9\x88\xf40\xef\xed\x8b'\x13\xbc\xa5\xccYGb\xc2\x8db\x88lPs@)\x86v\xd7B\xf7\xd3X\x93\xc9\xf0\xfd\xae\xe0`j#\x0b\xca;\xf8", b'\x00\x11\x8aEL3\x839E\xbd\xc4G\xd1xj\x0fxWu\xcb\xf6\xf3\xf2\x8e7!M\xca\x1c/\xd7\x7f\xed\xc6', b'\x02value1')
>>> get_witness_for_key_prefix(t.db, t.root_hash, b'key') # this will include additional nodes of b'key2'
(b'\x00\x82\x1a\xd9^L|38J\xed\xf31S\xb2\x97A\x8dy\x91RJ\x92\xf5ZC\xb4\x99T&;!\x9f\xa9!\xa2\xfe;', b"\x01*\xaccxH\x89\x08}\x93|\xda\xb9\r\x9b\x82\x8b\xb2Y\xbc\x10\xb9\x88\xf40\xef\xed\x8b'\x13\xbc\xa5\xccYGb\xc2\x8db\x88lPs@)\x86v\xd7B\xf7\xd3X\x93\xc9\xf0\xfd\xae\xe0`j#\x0b\xca;\xf8", b'\x00\x11\x8aEL3\x839E\xbd\xc4G\xd1xj\x0fxWu\xcb\xf6\xf3\xf2\x8e7!M\xca\x1c/\xd7\x7f\xed\xc6', b'\x02value1', b'\x00\x10O\xa9\x0b\x1c!_`<\xb5^\x98D\x89\x17\x148\xac\xda&\xb3P\xf6\x06[\x1b9\xc09\xbas\x85\xf5', b'\x02value2')
>>> get_witness_for_key_prefix(t.db, t.root_hash, b'') # this will return the whole trie