NEP 0 — Purpose and process#


Jarrod Millman <>







What is a NEP?#

NEP stands for NumPy Enhancement Proposal. A NEP is a design document providing information to the NumPy community, or describing a new feature for NumPy or its processes or environment. The NEP should provide a concise technical specification of the feature and a rationale for the feature.

We intend NEPs to be the primary mechanisms for proposing major new features, for collecting community input on an issue, and for documenting the design decisions that have gone into NumPy. The NEP author is responsible for building consensus within the community and documenting dissenting opinions.

Because the NEPs are maintained as text files in a versioned repository, their revision history is the historical record of the feature proposal [1].


There are three kinds of NEPs:

  1. A Standards Track NEP describes a new feature or implementation for NumPy.

  2. An Informational NEP describes a NumPy design issue, or provides general guidelines or information to the Python community, but does not propose a new feature. Informational NEPs do not necessarily represent a NumPy community consensus or recommendation, so users and implementers are free to ignore Informational NEPs or follow their advice.

  3. A Process NEP describes a process surrounding NumPy, or proposes a change to (or an event in) a process. Process NEPs are like Standards Track NEPs but apply to areas other than the NumPy language itself. They may propose an implementation, but not to NumPy’s codebase; they require community consensus. Examples include procedures, guidelines, changes to the decision-making process, and changes to the tools or environment used in NumPy development. Any meta-NEP is also considered a Process NEP.

NEP workflow#

The NEP process begins with a new idea for NumPy. It is highly recommended that a single NEP contain a single key proposal or new idea. Small enhancements or patches often don’t need a NEP and can be injected into the NumPy development workflow with a pull request to the NumPy repo. The more focused the NEP, the more successful it tends to be. If in doubt, split your NEP into several well-focused ones.

Each NEP must have a champion—someone who writes the NEP using the style and format described below, shepherds the discussions in the appropriate forums, and attempts to build community consensus around the idea. The NEP champion (a.k.a. Author) should first attempt to ascertain whether the idea is suitable for a NEP. Posting to the numpy-discussion mailing list is the best way to go about doing this.

The proposal should be submitted as a draft NEP via a GitHub pull request to the doc/neps directory with the name nep-<n>.rst where <n> is an appropriately assigned four-digit number (e.g., nep-0000.rst). The draft must use the NEP X — Template and instructions file.

Once the PR for the NEP is in place, a post should be made to the mailing list containing the sections up to “Backward compatibility”, with the purpose of limiting discussion there to usage and impact. Discussion on the pull request will have a broader scope, also including details of implementation.

At the earliest convenience, the PR should be merged (regardless of whether it is accepted during discussion). Additional PRs may be made by the Author to update or expand the NEP, or by maintainers to set its status, discussion URL, etc.

Standards Track NEPs consist of two parts, a design document and a reference implementation. It is generally recommended that at least a prototype implementation be co-developed with the NEP, as ideas that sound good in principle sometimes turn out to be impractical when subjected to the test of implementation. Often it makes sense for the prototype implementation to be made available as PR to the NumPy repo (making sure to appropriately mark the PR as a WIP).

Review and resolution#

NEPs are discussed on the mailing list. The possible paths of the status of NEPs are as follows:


All NEPs should be created with the Draft status.

Eventually, after discussion, there may be a consensus that the NEP should be accepted – see the next section for details. At this point the status becomes Accepted.

Once a NEP has been Accepted, the reference implementation must be completed. When the reference implementation is complete and incorporated into the main source code repository, the status will be changed to Final.

To allow gathering of additional design and interface feedback before committing to long term stability for a language feature or standard library API, a NEP may also be marked as “Provisional”. This is short for “Provisionally Accepted”, and indicates that the proposal has been accepted for inclusion in the reference implementation, but additional user feedback is needed before the full design can be considered “Final”. Unlike regular accepted NEPs, provisionally accepted NEPs may still be Rejected or Withdrawn even after the related changes have been included in a Python release.

Wherever possible, it is considered preferable to reduce the scope of a proposal to avoid the need to rely on the “Provisional” status (e.g. by deferring some features to later NEPs), as this status can lead to version compatibility challenges in the wider NumPy ecosystem.

A NEP can also be assigned status Deferred. The NEP author or a core developer can assign the NEP this status when no progress is being made on the NEP.

A NEP can also be Rejected. Perhaps after all is said and done it was not a good idea. It is still important to have a record of this fact. The Withdrawn status is similar—it means that the NEP author themselves has decided that the NEP is actually a bad idea, or has accepted that a competing proposal is a better alternative.

When a NEP is Accepted, Rejected, or Withdrawn, the NEP should be updated accordingly. In addition to updating the status field, at the very least the Resolution header should be added with a link to the relevant thread in the mailing list archives.

NEPs can also be Superseded by a different NEP, rendering the original obsolete. The Replaced-By and Replaces headers containing references to the original and new NEPs, like :ref:`NEP#number` should be added respectively.

Process NEPs may also have a status of Active if they are never meant to be completed, e.g. NEP 0 (this NEP).

How a NEP becomes accepted#

A NEP is Accepted by consensus of all interested contributors. We need a concrete way to tell whether consensus has been reached. When you think a NEP is ready to accept, send an email to the numpy-discussion mailing list with a subject like:

Proposal to accept NEP #<number>: <title>

In the body of your email, you should:

  • link to the latest version of the NEP,

  • briefly describe any major points of contention and how they were resolved,

  • include a sentence like: “If there are no substantive objections within 7 days from this email, then the NEP will be accepted; see NEP 0 for more details.”

For an example, see:

After you send the email, you should make sure to link to the email thread from the Discussion section of the NEP, so that people can find it later.

Generally the NEP author will be the one to send this email, but anyone can do it – the important thing is to make sure that everyone knows when a NEP is on the verge of acceptance, and give them a final chance to respond. If there’s some special reason to extend this final comment period beyond 7 days, then that’s fine, just say so in the email. You shouldn’t do less than 7 days, because sometimes people are travelling or similar and need some time to respond.

In general, the goal is to make sure that the community has consensus, not provide a rigid policy for people to try to game. When in doubt, err on the side of asking for more feedback and looking for opportunities to compromise.

If the final comment period passes without any substantive objections, then the NEP can officially be marked Accepted. You should send a followup email notifying the list (celebratory emoji optional but encouraged 🎉✨), and then update the NEP by setting its :Status: to Accepted, and its :Resolution: header to a link to your followup email.

If there are substantive objections, then the NEP remains in Draft state, discussion continues as normal, and it can be proposed for acceptance again later once the objections are resolved.

In unusual cases, the NumPy Steering Council may be asked to decide whether a controversial NEP is Accepted.


In general, Standards track NEPs are no longer modified after they have reached the Final state as the code and project documentation are considered the ultimate reference for the implemented feature. However, finalized Standards track NEPs may be updated as needed.

Process NEPs may be updated over time to reflect changes to development practices and other details. The precise process followed in these cases will depend on the nature and purpose of the NEP being updated.

Format and template#

NEPs are UTF-8 encoded text files using the reStructuredText format. Please see the NEP X — Template and instructions file and the reStructuredTextPrimer for more information. We use Sphinx to convert NEPs to HTML for viewing on the web [2].

Header Preamble#

Each NEP must begin with a header preamble. The headers must appear in the following order. Headers marked with * are optional. All other headers are required.

  :Author: <list of authors' real names and optionally, email addresses>
  :Status: <Draft | Active | Accepted | Deferred | Rejected |
           Withdrawn | Final | Superseded>
  :Type: <Standards Track | Process>
  :Created: <date created on, in dd-mmm-yyyy format>
* :Requires: <nep numbers>
* :NumPy-Version: <version number>
* :Replaces: <nep number>
* :Replaced-By: <nep number>
* :Resolution: <url>

The Author header lists the names, and optionally the email addresses of all the authors of the NEP. The format of the Author header value must be

Random J. User <[email protected]>

if the email address is included, and just

Random J. User

if the address is not given. If there are multiple authors, each should be on a separate line.


References and footnotes#