Contributing to Pyomo

We welcome all contributions including bug fixes, feature enhancements, and documentation improvements. Pyomo manages source code contributions via GitHub pull requests (PRs).

Contribution Requirements

A PR should be 1 set of related changes. PRs for large-scale non-functional changes (i.e. PEP8, comments) should be separated from functional changes. This simplifies the review process and ensures that functional changes aren’t obscured by large amounts of non-functional changes.

Coding Standards

  • Required: 4 space indentation (no tabs)
  • Desired: PEP8
  • No use of __author__
  • Inside pyomo.contrib: Contact information for the contribution maintainer (such as a Github ID) should be included in the Sphinx documentation

Sphinx-compliant documentation is required for:

  • Modules
  • Public and Private Classes
  • Public and Private Functions

We also encourage you to include examples, especially for new features and contributions to pyomo.contrib.


Pyomo uses unittest, TravisCI, and Appveyor for testing and continuous integration. Submitted code should include tests to establish the validity of its results and/or effects. Unit tests are preferred but we also accept integration tests. When test are run on a PR, we require at least 70% coverage of the lines modified in the PR and prefer coverage closer to 90%. We also require that all tests pass before a PR will be merged.

At any point in the development cycle, a “work in progress” pull request may be opened by including ‘[WIP]’ at the beginning of the PR title. This allows your code changes to be tested by Pyomo’s automatic testing infrastructure. Any pull requests marked ‘[WIP]’ will not be reviewed or merged by the core development team. In addition, any ‘[WIP]’ pull request left open for an extended period of time without active development may be marked ‘stale’ and closed.

Review Process

After a PR is opened it will be reviewed by at least two members of the core development team. The core development team consists of anyone with write-access to the Pyomo repository. Pull requests opened by a core developer only require one review. The reviewers will decide if they think a PR should be merged or if more changes are necessary.

Reviewers look for:

  • Outside of pyomo.contrib: Code rigor and standards, edge cases, side effects, etc.
  • Inside of pyomo.contrib: No “glaringly obvious” problems with the code
  • Documentation and tests

The core development team tries to review pull requests in a timely manner but we make no guarantees on review timeframes. In addition, PRs might not be reviewed in the order they are opened in.

Where to put contributed code

In order to contribute to Pyomo, you must first make a fork of the Pyomo git repository. Next, you should create a branch on your fork dedicated to the development of the new feature or bug fix you’re interested in. Once you have this branch checked out, you can start coding. Bug fixes and minor enhancements to existing Pyomo functionality should be made in the appropriate files in the Pyomo code base. New examples, features, and packages built on Pyomo should be placed in pyomo.contrib. Follow the link below to find out if pyomo.contrib is right for your code.


Pyomo uses the pyomo.contrib package to facilitate the inclusion of third-party contributions that enhance Pyomo’s core functionality. The are two ways that pyomo.contrib can be used to integrate third-party packages:

  • pyomo.contrib can provide wrappers for separate Python packages, thereby allowing these packages to be imported as subpackages of pyomo.
  • pyomo.contrib can include contributed packages that are developed and maintained outside of the Pyomo developer team.

Including contrib packages in the Pyomo source tree provides a convenient mechanism for defining new functionality that can be optionally deployed by users. We expect this mechanism to include Pyomo extensions and experimental modeling capabilities. However, contrib packages are treated as optional packages, which are not maintained by the Pyomo developer team. Thus, it is the responsibility of the code contributor to keep these packages up-to-date.

Contrib package contributions will be considered as pull-requests, which will be reviewed by the Pyomo developer team. Specifically, this review will consider the suitability of the proposed capability, whether tests are available to check the execution of the code, and whether documentation is available to describe the capability. Contrib packages will be tested along with Pyomo. If test failures arise, then these packages will be disabled and an issue will be created to resolve these test failures.

The following two examples illustrate the two ways that pyomo.contrib can be used to integrate third-party contributions.

Including External Packages

The pyomocontrib_simplemodel package is derived from Pyomo, and it defines the class SimpleModel that illustrates how Pyomo can be used in a simple, less object-oriented manner. Specifically, this class mimics the modeling style supported by PuLP.

While pyomocontrib_simplemodel can be installed and used separate from Pyomo, this package is included in pyomo/contrib/simplemodel. This allows this package to be referenced as if were defined as a subpackage of pyomo.contrib. For example:

from pyomo.contrib.simplemodel import *
from math import pi

m = SimpleModel()

r = m.var('r', bounds=(0,None))
h = m.var('h', bounds=(0,None))

m += 2*pi*r*(r + h)
m += pi*h*r**2 == 355

status = m.solve("ipopt")

This example illustrates that a package can be distributed separate from Pyomo while appearing to be included in the pyomo.contrib subpackage. Pyomo requires a separate directory be defined under pyomo/contrib for each such package, and the Pyomo developer team will approve the inclusion of third-party packages in this manner.

Contrib Packages within Pyomo

Third-party contributions can also be included directly within the pyomo.contrib package. The pyomo/contrib/example package provides an example of how this can be done, including a directory for plugins and package tests. For example, this package can be imported as a subpackage of pyomo.contrib:

from pyomo.environ import *
from pyomo.contrib.example import a

# Print the value of 'a' defined by this package

Although pyomo.contrib.example is included in the Pyomo source tree, it is treated as an optional package. Pyomo will attempt to import this package, but if an import failure occurs, Pyomo will silently ignore it. Otherwise, this pyomo package will be treated like any other. Specifically:

  • Plugin classes defined in this package are loaded when pyomo.environ is loaded.
  • Tests in this package are run with other Pyomo tests.