---
id: toposort
version: "1.10"
license: Apache License Version 2.0
license_treatment: permissive
maintenance: abandoned
---

# toposort — Implements a topological sort algorithm.

License: permissive · Maintenance: abandoned · Downloads: 13.0M/mo

## What it is and what it does

toposort is a pure Python implementation of the topological sorting algorithm. It takes a dictionary where each key is a node and its value is a set of nodes it depends on, then returns an iterator of sets representing valid processing orders—nodes with no remaining dependencies come first. If a circular dependency exists, it raises CyclicDependencyError with details about the cycle.

The package is straightforward and self-contained, with no external runtime dependencies. It supports both granular iteration (toposort) and flattened output (toposort_flatten), making it suitable for build systems, task scheduling, and any workflow requiring dependency resolution. The implementation handles arbitrary hashable node types, not just integers.

Use it for:

- Determine build order for interdependent software modules or packages.
- Schedule task execution respecting prerequisite constraints in workflow systems.
- Resolve import or initialization order in complex codebases with circular-dependency detection.
- Order database migrations or schema changes based on foreign-key dependencies.
- Compute execution order for computation graphs in data pipelines.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Implements topological sorting of directed acyclic graphs, ordering nodes so dependencies are processed before dependents.

Yes, if you need a simple, dependency-free topological sort. The algorithm is stable and well-tested (Production/Stable status), and the abandoned maintenance status poses minimal risk for a mature, narrow-scope library. Use it for straightforward dependency ordering; if you need advanced graph algorithms or active support, consider alternatives.

## Install

pip install toposort
uv add toposort
poetry add toposort

## Installing toposort

Before you install: Low install friction with no runtime dependencies. Package is marked abandoned (last release 2023-02-25, 1266 days ago), so expect no active maintenance or bug fixes.

License in practice: Apache License 2.0 (permissive) allows use in most projects without significant restrictions.

Quickstart:

from toposort import toposort, toposort_flatten

data = {2: {11}, 9: {11, 8, 10}, 10: {11, 3}, 11: {7, 5}, 8: {7, 3}}
result = list(toposort(data))
flat = toposort_flatten(data)

Verify before relying:

- Whether the abandoned status affects reliability for stable, well-tested algorithms like topological sort.
- Performance characteristics on large graphs or whether there are known limitations in the implementation.

## Package facts

- License: Apache License Version 2.0 (permissive)
- Python support: unspecified
- Install friction: low
- Maintenance: abandoned
- Downloads: 13.0M/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

topological sort, dependency ordering, directed acyclic graph, toposort algorithm, process dependencies in order, circular dependency detection, node ordering, graph-algorithms, dependency-resolution

[View on SkillFed](https://skillfed.io/packages/toposort) · [View on PyPI](https://pypi.org/project/toposort/)