pygtrie 2.5.0
A pure Python trie data structure implementation.
License: Apache-2.0
Keywords: trie,prefix tree,data structure

pygtrie
=======

pygtrie is a pure Python implementation of a trie data structure
compatible with Python 2.x and Python 3.x.

`Trie data structure <http://en.wikipedia.org/wiki/Trie>`_, also known
as radix or prefix tree, is a tree associating keys to values where
all the descendants of a node have a common prefix (associated with
that node).

The trie module contains ``Trie``, ``CharTrie`` and ``StringTrie``
classes each implementing a mutable mapping interface, i.e. ``dict``
interface.  As such, in most circumstances, ``Trie`` could be used as
a drop-in replacement for a ``dict``, but the prefix nature of the
data structure is trie’s real strength.

The module also contains ``PrefixSet`` class which uses a trie to
store a set of prefixes such that a key is contained in the set if it
or its prefix is stored in the set.

Features
--------

- A full mutable mapping implementation.

- Supports iterating over as well as deleting a subtrie.

- Supports prefix checking as well as shortest and longest prefix
  look-up.

- Extensible for any kind of user-defined keys.

- A PrefixSet supports “all keys starting with given prefix” logic.

- Can store any value including None.

Installation
------------

To install pygtrie, simply run::

    pip install pygtrie

or by adding line such as::

    pygtrie == 2.*

to project’s `requirements file
<https://pip.pypa.io/en/latest/user_guide/#requirements-files>`_.
Alternatively, if installation from source is desired, it can be
achieved by executing::

    python setup.py install

Version History
---------------

2.5: 2022/07/16

- Add ``pygtrie.Trie.merge`` method which merges structures of two
  tries.

- Add ``pygtrie.Trie.strictly_equals`` method which compares two
  tries with stricter rules than regular equality operator.  It’s not
  sufficient that keys and values are the same but the structure of
  the tries must be the same as well.  For example:

      >>> t0 = StringTrie({'foo/bar.baz': 42}, separator='/')
      >>> t1 = StringTrie({'foo/bar.baz': 42}, separator='.')
      >>> t0 == t1
      True
      >>> t0.strictly_equals(t1)
      False

- Fix ``pygtrie.Trie.__eq__`` implementation such that key values
  are taken into consideration rather than just looking at trie
  structure.  To see what this means it’s best to look at a few
  examples.  Firstly:

      >>> t0 = StringTrie({'foo/bar': 42}, separator='/')
      >>> t1 = StringTrie({'foo.bar': 42}, separator='.')
      >>> t0 == t1
      False

  This used to be true since the two tries have the same node
  structure.  However, as far as Mapping interface is concerned, they
  use different keys, i.e. ```set(t0) != set(t1)``.  Secondly:

      >>> t0 = StringTrie({'foo/bar.baz': 42}, separator='/')
      >>> t1 = StringTrie({'foo/bar.baz': 42}, separator='.')
      >>> t0 == t1
      True

  This used to be false since the two tries have different node
  structures (the first one splits key into ``('foo', 'bar.baz')``
  while the second into ``('foo/bar', 'baz')``).  However, their keys
  are the same, i.e. ```set(t0) == set(t1)``.  And lastly:

      >>> t0 = Trie({'foo': 42})
      >>> t1 = CharTrie({'foo': 42})
      >>> t0 == t1
      False

  This used to be true since the two tries have the same node
  structure.  However, the two classes return key as different values.
  ``pygtrie.Trie`` returns keys as tuples while
  ``pygtrie.CharTrie`` returns them as strings.

2.4.2: 2021/01/03

- Remove use of ‘super’ in ``setup.py`` to fix compatibility with
  Python 2.7.  This changes build code only; no changes to the library
  itself.

2.4.1: 2020/11/20

- Remove dependency on ``packaging`` module from ``setup.py`` to fix
  installation on systems without that package.  This changes build
  code only; no changes to the library itself.  [Thanks to Eric
  McLachlan for reporting]

2.4.0: 2020/11/19  [pulled back from PyPi]

- Change ``children`` argument of the ``node_factory`` passed to
  ``pygtrie.Trie.traverse`` from a generator to an iterator with
  a custom bool conversion.  This allows checking whether node has
  children without having to iterate over them (``bool(children)``)

  To test whether this feature is available, one can check whether
  `Trie.traverse.uses_bool_convertible_children` property is true,
  e.g.: ``getattr(pygtrie.Trie.traverse,
  'uses_bool_convertible_children', False)``.

  [Thanks to Pallab Pain for suggesting the feature]

2.3.3: 2020/04/04

- Fix to ‘``AttributeError``: ``_NoChildren`` object has no
  attribute ``sorted_items``’ failure when iterating over a trie with
  sorting enabled.  [Thanks to Pallab Pain for reporting]

- Add ``value`` property setter to step objects returned by
  ``pygtrie.Trie.walk_towards`` et al.  This deprecates the
  ``set`` method.

- The module now exports `pygtrie.__version__` making it possible to
  determine version of the library at run-time.

2.3.2: 2019/07/18

- Trivial metadata fix

2.3.1: 2019/07/18  [pulled back from PyPi]

- Fix to ``pygtrie.PrefixSet`` initialisation incorrectly storing
  elements even if their prefixes are also added to the set.

  For example, ``PrefixSet(('foo', 'foobar'))`` incorrectly resulted
  in a two-element set even though the interface dictates that only
  ``foo`` is kept (recall that if ``foo`` is member of the set,
  ``foobar`` is as well).  [Thanks to Tal Maimon for reporting]

- Fix to ``pygtrie.Trie.copy`` method not preserving
  enable-sorting flag and, in case of ``pygtrie.StringTrie``,
  ``separator`` property.

- Add support for the ``copy`` module so ``copy.copy`` can now be
  used with trie objects.

- Leafs and nodes with just one child use more memory-optimised
  representation which reduces overall memory usage of a trie
  structure.

- Minor performance improvement for adding new elements to
  a ``pygtrie.PrefixSet``.

- Improvements to string representation of objects which now includes
  type and, for ``pygtrie.StringTrie`` object, value of separator
  property.

2.3: 2018/08/10

- New ``pygtrie.Trie.walk_towards`` method allows walking a path
  towards a node with given key accessing each step of the path.
  Compared to `pygtrie.Trie.walk_prefixes` method, steps for nodes
  without assigned values are returned.

- Fix to ``pygtrie.PrefixSet.copy`` not preserving type of backing
  trie.

- ``pygtrie.StringTrie`` now checks and explicitly rejects empty
  separators.  Previously empty separator would be accepted but lead
  to confusing errors later on.  [Thanks to Waren Long]

- Various documentation improvements, Python 2/3 compatibility and
  test coverage (python-coverage reports 100%).