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Python Enhancement Proposals

PEP 503 – Simple Repository API

Donald Stufft <donald at>
Donald Stufft <donald at>
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There are many implementations of a Python package repository and many tools that consume them. Of these, the canonical implementation that defines what the “simple” repository API looks like is the implementation that powers PyPI. This document will specify that API, documenting what the correct behavior for any implementation of the simple repository API.


A repository that implements the simple API is defined by its base URL, this is the top level URL that all additional URLs are below. The API is named the “simple” repository due to the fact that PyPI’s base URL is


All subsequent URLs in this document will be relative to this base URL (so given PyPI’s URL, a URL of /foo/ would be

Within a repository, the root URL (/ for this PEP which represents the base URL) MUST be a valid HTML5 page with a single anchor element per project in the repository. The text of the anchor tag MUST be the name of the project and the href attribute MUST link to the URL for that particular project. As an example:

<!DOCTYPE html>
    <a href="/frob/">frob</a>
    <a href="/spamspamspam/">spamspamspam</a>

Below the root URL is another URL for each individual project contained within a repository. The format of this URL is /<project>/ where the <project> is replaced by the normalized name for that project, so a project named “HolyGrail” would have a URL like /holygrail/. This URL must respond with a valid HTML5 page with a single anchor element per file for the project. The href attribute MUST be a URL that links to the location of the file for download, and the text of the anchor tag MUST match the final path component (the filename) of the URL. The URL SHOULD include a hash in the form of a URL fragment with the following syntax: #<hashname>=<hashvalue>, where <hashname> is the lowercase name of the hash function (such as sha256) and <hashvalue> is the hex encoded digest.

In addition to the above, the following constraints are placed on the API:

  • All URLs which respond with an HTML5 page MUST end with a / and the repository SHOULD redirect the URLs without a / to add a / to the end.
  • URLs may be either absolute or relative as long as they point to the correct location.
  • There are no constraints on where the files must be hosted relative to the repository.
  • There may be any other HTML elements on the API pages as long as the required anchor elements exist.
  • Repositories MAY redirect unnormalized URLs to the canonical normalized URL (e.g. /Foobar/ may redirect to /foobar/), however clients MUST NOT rely on this redirection and MUST request the normalized URL.
  • Repositories SHOULD choose a hash function from one of the ones guaranteed to be available via the hashlib module in the Python standard library (currently md5, sha1, sha224, sha256, sha384, sha512). The current recommendation is to use sha256.
  • If there is a GPG signature for a particular distribution file it MUST live alongside that file with the same name with a .asc appended to it. So if the file /packages/HolyGrail-1.0.tar.gz existed and had an associated signature, the signature would be located at /packages/HolyGrail-1.0.tar.gz.asc.
  • A repository MAY include a data-gpg-sig attribute on a file link with a value of either true or false to indicate whether or not there is a GPG signature. Repositories that do this SHOULD include it on every link.
  • A repository MAY include a data-requires-python attribute on a file link. This exposes the Requires-Python metadata field, specified in PEP 345, for the corresponding release. Where this is present, installer tools SHOULD ignore the download when installing to a Python version that doesn’t satisfy the requirement. For example:
    <a href="..." data-requires-python="&gt;=3">...</a>

    In the attribute value, < and > have to be HTML encoded as &lt; and &gt;, respectively.

Normalized Names

This PEP references the concept of a “normalized” project name. As per PEP 426 the only valid characters in a name are the ASCII alphabet, ASCII numbers, ., -, and _. The name should be lowercased with all runs of the characters ., -, or _ replaced with a single - character. This can be implemented in Python with the re module:

import re

def normalize(name):
    return re.sub(r"[-_.]+", "-", name).lower()


  • The optional data-requires-python attribute was added in July 2016.


Last modified: 2023-09-09 17:39:29 GMT