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Python Enhancement Proposals

PEP 700 – Additional Fields for the Simple API for Package Indexes

Paul Moore <p.f.moore at>
Donald Stufft <donald at>
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Standards Track
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Table of Contents


This PEP is a historical document. The up-to-date, canonical spec, Simple repository API, is maintained on the PyPA specs page.


See the PyPA specification update process for how to propose changes.


PEP 691 defined a JSON form for the “Simple Repository API”. This allowed clients to more easily query the data that was previously only available in HTML, as defined in PEP 503.

This proposal adds three fields to the JSON form, which allow it to be used in place of PyPI’s JSON API in a number of situations.

  • A field to allow retrieval of a list of all the published versions of a project.
  • Fields containing the size and upload time for a project file.

The new fields are all part of the data returned from the “project details” URL.


With the introduction of the JSON form of the simple API in PEP 691, the simple API offers functionality that is almost as complete as the PyPI JSON API. This PEP adds a number of fields which were previously only available through the JSON API, in order to allow more clients which were previously Warehouse specific to support arbitrary standards-compliant indexes.


This specification defines version 1.1 of the simple repository API. For the HTML version of the API, there is no change from version 1.0. For the JSON version of the API, the following changes are made:

  • The api-version must specify version 1.1 or later.
  • A new versions key is added at the top level.
  • Two new “file information” keys, size and upload-time, are added to the files data.
  • Keys (at any level) with a leading underscore are reserved as private for index server use. No future standard will assign a meaning to any such key.

The versions and size keys are mandatory. The upload-time key is optional.


An additional key, versions MUST be present at the top level, in addition to the keys name, files and meta defined in PEP 691. This key MUST contain a list of version strings specifying all of the project versions uploaded for this project. The value is logically a set, and as such may not contain duplicates, and the order of the values is not significant.

All of the files listed in the files key MUST be associated with one of the versions in the versions key. The versions key MAY contain versions with no associated files (to represent versions with no files uploaded, if the server has such a concept).

Note that because servers may hold “legacy” data from before the adoption of PEP 440, version strings currently cannot be required to be valid PEP 440 versions, and therefore cannot be assumed to be orderable using the PEP 440 rules. However, servers SHOULD use normalised PEP 440 versions where possible.

Additional file information

Two new keys are added to the files key.

  • size: This field is mandatory. It MUST contain an integer which is the file size in bytes.
  • upload-time: This field is optional. If present, it MUST contain a valid ISO 8601 date/time string, in the format yyyy-mm-ddThh:mm:ss.ffffffZ, which represents the time the file was uploaded to the index. As indicated by the Z suffix, the upload time MUST use the UTC timezone. The fractional seconds part of the timestamp (the .ffffff part) is optional, and if present may contain up to 6 digits of precision. If a server does not record upload time information for a file, it MAY omit the upload-time key.


Why not add this data to the HTML API as well?

It would be possible to add the data to the HTML API, but the vast majority of consumers for this data are likely to be currently getting it from the PyPI JSON API, and so will already be expecting to parse JSON. Traditional consumers of the HTML API have never needed this data previously.

Does this imply that the HTML API is obsolete?

No. The FAQ of PEP 691 was clear that the HTML API is not being deprecated, and this PEP does not change that position. However, clients wishing to access the new data introduced by this PEP will need to use the JSON API to get it. And indexes wanting to provide it will need to serve the JSON format.

Is the simple API replacing the Warehouse JSON and XML-RPC APIs?

Where possible, clients should prefer the simple API over the JSON or XML-RPC APIs, as the former is standardised and can be assumed to be available from any index, whereas the latter are exclusive to the Warehouse project.

However, while this PEP brings the simple API closer to being able to replace the JSON API, there is no formal policy that the simple API will replicate all of the functionality covered by the existing Warehouse APIs. Proposed additions to the simple API will still be considered on their individual merits, and the requirement that the API should be simple and fast for the primary use case of locating files for a project will remain the overriding consideration.

Why not allow other date formats?

The ISO 8601 standard is complex, and there seems little value in requiring clients to deal with that. The standard library datetime module provides methods to parse ISO 8601 strings, but it is possible that users may want to access index data without using Python (for example, piping the output of curl into jq). Having a single, well-defined format makes this easier, and doesn’t have any significant disadvantages.

What if file sizes are too big for a JSON number?

The JSON standard does not specify how numbers are to be interpreted. Python can read and write arbitrary-length integers in a JSON file, so this should not be an issue for code written in Python. Non-Python implementations may need to take care to handle large integers correctly, but this is not expected to be a significant problem.

Why not require PEP 440 versions?

At the time this PEP was written, PyPI still contains (and serves) projects and files with “legacy” versions. Requiring PEP 440 versions would make it impossible for PyPI to follow this specification while still serving the existing content.

Ideally, at some future time, the simple index API will be updated to require PEP 440 versions, at which time this specification should be updated to reflect that. However, that change will need to be co-ordinated with existing index providers including PyPI, to desupport and remove non-conforming projects and/or files.

Why not provide a “latest version” value?

For PEP 440 versions, this is easy enough for the client to do (using the packaging library, latest = max(Version(s) for s in proj["versions"])). For non-standard versions, there is no well-defined ordering, and clients will need to decide on what rule is appropriate for their needs. Requiring the server to supply a latest version value takes the choice away from the client.

Servers with an explicit concept of which version is the “latest”, which cannot be calculated from data available to the client, can provide a non-standard, underscore-prefixed key to convey that information to the client if they wish.


Last modified: 2024-03-24 15:15:52 GMT