PDEP-1: Purpose and guidelines

PDEP definition, purpose and scope

A PDEP (pandas enhancement proposal) is a proposal for a major change in pandas, in a similar way as a Python PEP or a NumPy NEP.

Bug fixes and conceptually minor changes (e.g. adding a parameter to a function) are out of the scope of PDEPs. A PDEP should be used for changes that are not immediate and not obvious, and are expected to require a significant amount of discussion and require detailed documentation before being implemented.

PDEP are appropriate for user facing changes, internal changes and organizational discussions. Examples of topics worth a PDEP could include moving a module from pandas to a separate repository, a refactoring of the pandas block manager or a proposal of a new code of conduct.

PDEP guidelines

Target audience

A PDEP is a public document available to anyone, but the main stakeholders to consider when writing a PDEP are:

PDEP authors

Anyone can propose a PDEP, but in most cases developers of pandas itself and related projects are expected to author PDEPs. If you are unsure if you should be opening an issue or creating a PDEP, it's probably safe to start by opening an issue, which can be eventually moved to a PDEP.


The possible states of a PDEP are:

Next is described the workflow that PDEPs can follow.

Submitting a PDEP

Proposing a PDEP is done by creating a PR adding a new file to web/pdeps/. The file is a markdown file, you can use web/pdeps/0001.md as a reference for the expected format.

The initial status of a PDEP will be Status: Under discussion. This will be changed to Status: Accepted when the PDEP is ready and have the approval of the core team.

Accepted PDEP

A PDEP can only be accepted by the core development team, if the proposal is considered worth implementing. Decisions will be made based on the process detailed in the pandas governance document. In general, more than one approval will be needed before the PR is merged. And there should not be any Request changes review at the time of merging.

Once a PDEP is accepted, any contributions can be made toward the implementation of the PDEP, with an open-ended completion timeline. Development of pandas is difficult to understand and forecast, being that the contributors to pandas are a mix of volunteers and developers paid from different sources, with different priorities. For companies, institutions or individuals with interest in seeing a PDEP being implemented, or to in general see progress to the pandas roadmap, please check how you can help in the contributing page.

Implemented PDEP

Once a PDEP is implemented and available in the main branch of pandas, its status will be changed to Status: Implemented, so there is visibility that the PDEP is not part of the roadmap and future plans, but a change that has already happened. The first pandas version in which the PDEP implementation is available will also be included in the PDEP header with for example Implemented: v2.0.0.

Rejected PDEP

A PDEP can be rejected when the final decision is that its implementation is not in the best interests of the project. Rejected PDEPs are as useful as accepted PDEPs, since there are discussions that are worth having, and decisions about changes to pandas being made. They will be merged with Status: Rejected, so there is visibility on what was discussed and what was the outcome of the discussion. A PDEP can be rejected for different reasons, for example good ideas that aren't backward-compatible, and the breaking changes aren't considered worth implementing.

Invalid PDEP

For submitted PDEPs that do not contain proper documentation, are out of scope, or are not useful to the community for any other reason, the PR will be closed after discussion with the author, instead of merging them as rejected. This is to avoid adding noise to the list of rejected PDEPs, which should contain documentation as good as an accepted PDEP, but where the final decision was to not implement the changes.

Evolution of PDEPs

Most PDEPs aren't expected to change after accepted. Once there is agreement in the changes, and they are implemented, the PDEP will be only useful to understand why the development happened, and the details of the discussion.

But in some cases, a PDEP can be updated. For example, a PDEP defining a procedure or a policy, like this one (PDEP-1). Or cases when after attempting the implementation, new knowledge is obtained that makes the original PDEP obsolete, and changes are required. When there are specific changes to be made to the original PDEP, this will be edited, its Revision: X label will be increased by one, and a note will be added to the PDEP-N history section. This will let readers understand that the PDEP has changed and avoid confusion.

PDEP-1 History