Environment:Pyro ppl Pyro Funsor Backend

Knowledge Sources	Pyro Funsor
Domains	Infrastructure, Probabilistic_Programming
Last Updated	2026-02-09 09:00 GMT

Overview

Optional Funsor backend environment providing an alternative inference engine for discrete variable enumeration and the AutoGaussian guide family.

Description

Funsor is a tensor-based functional programming library that provides an alternative backend for Pyro's discrete enumeration and Gaussian guide computations. It is pinned to an exact version (0.4.4) to ensure compatibility. Funsor is required specifically for `CollapseMessenger` (experimental collapsed inference), the `AutoGaussianFunsor` guide, and the `contrib.funsor` enumeration backend.

Usage

Use this environment when using the AutoGaussian guide with funsor backend, CollapseMessenger for collapsed inference, or the contrib.funsor enumeration backend for discrete variable models.

System Requirements

Category	Requirement	Notes
Python	>= 3.8	Same as core Pyro requirement
Hardware	CPU (minimum)	Same as core environment

Dependencies

Python Packages

`funsor[torch]` == 0.4.4 (exactly pinned)

Credentials

No credentials required.

Quick Install

# Install Pyro with Funsor backend
pip install pyro-ppl[funsor]

# This installs funsor[torch]==0.4.4

Code Evidence

Exact version pin from `setup.py:143-145`:

"funsor": [
    "funsor[torch]==0.4.4",
],

Funsor import guard in `pyro/poutine/collapse_messenger.py:17-28`:

# TODO Remove import guard once funsor is a required dependency.
try:
    import funsor
    from funsor.cnf import Contraction
    from funsor.delta import Delta
    from funsor.terms import Funsor, Variable
except ImportError:
    # Create fake types for singledispatch.
    Contraction = type("Contraction", (), {})
    Delta = type("Delta", (), {})
    Funsor = type("Funsor", (), {})
    Variable = type("Variable", (), {})

AutoGaussian funsor import with helpful error from `pyro/infer/autoguide/gaussian.py:616-625`:

def _import_funsor():
    try:
        import funsor
    except ImportError as e:
        raise ImportError(
            'AutoGaussian(..., backend="funsor") requires funsor. '
            "Try installing via: pip install pyro-ppl[funsor]"
        ) from e
    funsor.set_backend("torch")
    return funsor

Conditional registration in `pyro/contrib/__init__.py:35-42`:

try:
    import funsor as funsor_  # noqa: F401
    from pyro.contrib import funsor
    __all__ += ["funsor"]
except ImportError:
    pass

Common Errors

Error Message	Cause	Solution
`ImportError: AutoGaussian(..., backend="funsor") requires funsor`	Funsor not installed	`pip install pyro-ppl[funsor]`
Version conflict with funsor	Wrong funsor version	Must use exactly `funsor[torch]==0.4.4`; uninstall and reinstall if needed
`ImportError` in CollapseMessenger	Funsor not available for collapsed inference	`pip install pyro-ppl[funsor]`; feature is experimental

Compatibility Notes

Exact version pin: Funsor is pinned to exactly 0.4.4; other versions are not guaranteed to work
Experimental: CollapseMessenger with Funsor is marked experimental (note the TODO comment about making funsor a required dependency)
Backend initialization: Funsor must be initialized with `funsor.set_backend("torch")` before use; Pyro handles this internally

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