zss

library1.2.0pypypi✓ verified 85d ago

ZSS is a Python library that implements the Zhang-Shasha algorithm for computing the tree edit distance between two ordered labeled trees. It is currently at version 1.2.0 and, while not frequently updated, provides a stable and specialized tool for comparing tree structures. The library can be extended with custom node formats and distance metrics, and optionally leverages `editdist` and `numpy` for enhanced functionality and performance.

data

pip install zss

package ↗

INSTALL

IMPORT

SIG · ZSS

zss

datapythonv1.2.0

Install

—

Import

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Disk

—

Pass rate

0/ 10

Env Coverage0 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v1.2.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

glibc

py 3.10

2/4 runs

py 3.11

2/4 runs

py 3.12

2/4 runs

py 3.13

2/4 runs

py 3.9

2/4 runs

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

simple_distance

✓ from zss import simple_distance

Node

✓ from zss import Node

distance

✓ from zss import distance

✗ from zss import simple_distance (for complex cost models)

`simple_distance` uses default insert/remove/update costs. For custom or asymmetric costs, use `zss.distance` with explicit cost functions.

This example demonstrates how to define two simple trees using the built-in `Node` class and compute their edit distance using `simple_distance()`. The `addkid` method is used to construct the tree structure.

from zss import simple_distance, Node A = ( Node("f") .addkid(Node("a") .addkid(Node("h")) .addkid(Node("c") .addkid(Node("l")) ) ) .addkid(Node("e")) ) B = ( Node("f") .addkid(Node("a") .addkid(Node("d")) .addkid(Node("c") .addkid(Node("b")) ) ) .addkid(Node("e")) ) distance = simple_distance(A, B) print(f"Tree edit distance: {distance}") # Expected: 2

Debug

Known issues

gotchaThe `simple_distance` function assumes default costs for node insertion, removal, and updates (based on label equality). If your application requires specific, non-uniform, or asymmetric costs, you must use the more general `zss.distance` function and provide custom `insert_cost`, `remove_cost`, and `update_cost` functions.

fix

Use `zss.distance(A, B, insert_cost=my_insert_cost, remove_cost=my_remove_cost, update_cost=my_update_cost)`.

affects: All versions

gotchaBy default, `zss` only knows how to handle nodes with string labels. When using custom tree structures or non-string labels, you must provide custom `get_children`, `get_label`, and `label_dist` functions to `simple_distance` or `distance`.

fix

Implement functions `get_children(node)`, `get_label(node)`, and `label_dist(label_a, label_b)` and pass them as arguments: `simple_distance(A, B, get_children=my_get_children, get_label=my_get_label, label_dist=my_label_dist)`.

affects: All versions

gotchaThe `editdist` and `numpy` packages are optional 'soft requirements'. Without `editdist`, label comparisons default to a simple equality check (0 if equal, 1 if not). Without `numpy`, performance can be significantly slower, especially for large trees.

fix

For optimal performance and accurate string-based label comparisons, ensure these packages are installed: `pip install zss editdist numpy`.

affects: All versions

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'zss'

The 'zss' package is not installed in the current Python environment, or the environment where it's installed is not active.

fix

Ensure the library is installed: `pip install zss`. If using a virtual environment, activate it before running your script.

TypeError: object of type 'MyCustomNode' has no len()

When using a custom node class instead of `zss.Node`, you haven't provided `get_children`, `get_label`, and/or `label_dist` functions to `zss.simple_distance` or `zss.distance`. The library tries to access attributes or methods it expects by default from `zss.Node`.

fix

Define functions to extract children and labels from your custom nodes, and a function to compare their labels. Then pass these to the distance calculation: `simple_distance(A, B, get_children=my_get_children_func, get_label=my_get_label_func, label_dist=my_label_distance_func)`.

AttributeError: 'Node' object has no attribute 'add_child'

The `zss.Node` class uses `addkid()` to add children, not a more generic `add_child()` or `append()` that might be common in other tree implementations.

fix

When building trees with `zss.Node`, use the `addkid()` method: `Node('parent').addkid(Node('child'))`.

Upgrade

Version history

1.2.0latest on PyPI · released Mar 12, 2018

Audit

Dependencies

editdistoptionalUses string edit distance to compare node labels rather than a simple equal/not-equal check, improving accuracy for string labels.

numpyoptionalSignificantly speeds up the library's computations, especially for larger trees. Requires numpy >= 1.7.

Agent activity

47 hits · last 30 days

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OpenAI (training)

Resources

packagehttps://pypi.org/project/zss/ ↗