Installation Guide¶

Requirements¶

Loman needs Python 3.11 or newer. Every release is tested against 3.11, 3.12, 3.13 and 3.14 on Linux, macOS and Windows.

Installing Loman¶

With uv¶

uv is the fastest way to install Loman, and the tool this project itself is built with. To add Loman to a project:

$ uv add loman

To install it into the environment you already have:

$ uv pip install loman

To try it without installing anything permanently — uv builds a throwaway environment and discards it afterwards:

$ uv run --with loman python

With pip¶

$ pip install loman

If you don't have pip installed, this Python installation guide will get you started.

With conda¶

Loman is published on PyPI rather than conda-forge, so install it with pip inside your conda environment:

$ conda create -n loman python=3.12
$ conda activate loman
$ pip install loman

Graphviz, however, is on conda-forge, which makes conda a convenient way to get it — see below.

Optional extras¶

Two features are packaged as extras, so a plain install stays small. Neither is needed for the core computation engine, and nothing in a bare import loman imports either one — both are loaded lazily, at the point you use the feature.

$ uv add 'loman[ui,efficient]'      # or: pip install 'loman[ui,efficient]'

efficient is a storage-format choice rather than a capability: without it, saved frames are written as .npy, which is numpy's own format and needs no extra package. Install it when you want the saved data readable by other tools; a frame pyarrow cannot represent falls back to the default encoding rather than failing the save.

Installing Graphviz¶

Loman draws dependency graphs by shelling out to Graphviz's dot command. The Python glue (pydotplus) is installed automatically with Loman, but the Graphviz binaries themselves are a separate, non-Python program that you need to install yourself — pip install loman cannot do it for you.

Everything else in Loman works without Graphviz; you only need it for the visualization features, for example Computation.draw() and the graph widget.

Install the binaries¶

Graphviz publishes packages for every major platform. Its official download page has full instructions, but for most people one of these one-liners is enough:

After installing, confirm the dot binary is on your PATH:

$ dot -V
dot - graphviz version 12.0.0 (...)

If that prints a version, Loman's visualization features are ready to use. If it reports that dot cannot be found, see the next section.

Windows: adding the Graphviz binary to your PATH¶

On Windows, some Graphviz installers place dot.exe in a directory that is not on your PATH, so Loman cannot find it even though Graphviz is installed. To fix this, locate dot.exe and add its directory to your PATH.

To find where dot.exe was installed, use the where command (it may not find it if the directory isn't yet on your PATH, in which case look under your Graphviz installation directory, typically C:\Program Files\Graphviz\bin):

C:\>where dot
C:\Program Files\Graphviz\bin\dot.exe

You can then add that bin directory to your PATH. The permanent fix is to add it through the Windows Environment Variables control panel. To set it just for the current Python session, you can run:

import os


def ensure_path(path):
    paths = os.environ["PATH"].split(";")
    if path not in paths:
        paths.append(path)
        os.environ["PATH"] = ";".join(paths)


ensure_path(r"C:\Program Files\Graphviz\bin")

Installing for development¶

Loman's development environment is managed by Rhiza, a template that supplies the Makefile, the CI workflows, the pre-commit hooks and the gates behind them. You do not need to install it: it is synced into the repository, and the Makefile is a thin shim that forwards to the rhiza-task CLI, fetched on demand through uvx.

So the whole setup is:

$ git clone https://github.com/janushendersonassetallocation/loman.git
$ cd loman
$ make install

make install creates the virtual environment, syncs every dependency group and extra from uv.lock, installs the pre-commit hooks, and runs the repository's own local-setup.sh — which installs Graphviz if it is missing, so the visualization tests can run. uv is installed automatically if you do not already have it.

Then:

$ make test     # the full suite, with coverage
$ make fmt      # the pre-commit hooks over every file
$ make all      # every gate CI runs
$ make help     # every available target

make help is worth running once: it lists the tasks Rhiza provides and, separately, the targets this repository adds in local.mk.

For what Rhiza is and where its own documentation lives, see Rhiza tooling.