PEP: 426 Title: Metadata for Python Software Packages 1.3 Version: $Revision$ Last-Modified: $Date$ Author: Daniel Holth Discussions-To: Distutils SIG Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 30 Aug 2012 Abstract ======== This PEP describes a mechanism for adding metadata to Python distributions. It includes specifics of the field names, and their semantics and usage. This document specifies version 1.3 of the metadata format. Version 1.0 is specified in PEP 241. Version 1.1 is specified in PEP 314. Version 1.2 is specified in PEP 345. Version 1.3 of the metadata format adds fields designed to make third-party packaging of Python Software easier and defines a formal extension mechanism. The fields are "Setup-Requires-Dist" "Provides-Extra", and "Extension". This version also adds the `extra` variable to the `environment markers` specification and allows the description to be placed into a payload section. Metadata Files ============== The syntax defined in this PEP is for use with Python distribution metadata files. The file format is a simple UTF-8 encoded Key: value format with no maximum line length, followed by a blank line and an arbitrary payload. The keys are case-insensitive. It is parseable by the ``email`` module with an appropriate ``email.policy.Policy()``. When ``metadata`` is a Unicode string, ```email.parser.Parser().parsestr(metadata)`` is a serviceable parser. There are two standard locations for these metadata files: * the ``PKG-INFO`` file included in the base directory of Python source distribution archives (as created by the distutils ``sdist`` command) * the ``.dist-info/METADATA`` files in a Python installation database, as described in PEP 376. Other tools involved in Python distribution may also use this format. Encoding ======== Metadata 1.3 files are UTF-8 with the restriction that keys must be ASCII. Parser implementations should be aware that older versions of the Metadata specification do not specify an encoding. Fields ====== This section specifies the names and semantics of each of the supported metadata fields. In a single Metadata 1.3 file, fields marked with "(optional)" may occur 0 or 1 times. Fields marked with "(multiple use)" may be specified 0, 1 or more times. Only "Metadata-Version", "Name", "Version", and "Summary" must appear exactly once. The fields may appear in any order within the file. Metadata-Version :::::::::::::::: Version of the file format; "1.3" is the only legal value. Example:: Metadata-Version: 1.3 Name :::: The name of the distribution. Example:: Name: BeagleVote Version ::::::: A string containing the distribution's version number. This field must be in the format specified in PEP 386. Example:: Version: 1.0a2 Summary ::::::: A one-line summary of what the distribution does. Example:: Summary: A module for collecting votes from beagles. Platform (multiple use) ::::::::::::::::::::::: A Platform specification describing an operating system supported by the distribution which is not listed in the "Operating System" Trove classifiers. See "Classifier" below. Examples:: Platform: ObscureUnix Platform: RareDOS Supported-Platform (multiple use) ::::::::::::::::::::::::::::::::: Binary distributions containing a metadata file will use the Supported-Platform field in their metadata to specify the OS and CPU for which the binary distribution was compiled. The semantics of the Supported-Platform field are not specified in this PEP. Example:: Supported-Platform: RedHat 7.2 Supported-Platform: i386-win32-2791 Description (optional, deprecated) :::::::::::::::::::::::::::::::::: A longer description of the distribution that can run to several paragraphs. Software that deals with metadata should not assume any maximum size for this field. The contents of this field can be written using reStructuredText markup [1]_. For programs that work with the metadata, supporting markup is optional; programs can also display the contents of the field as-is. This means that authors should be conservative in the markup they use. Since a line separator immediately followed by another line separator indicates the end of the headers section, any line separators in the description must be suffixed by whitespace to indicate continuation. Since Metadata 1.3 the recommended place for the description is in the payload section of the document, after the last header. The description does not need to be reformatted when it is included in the payload. Keywords (optional) ::::::::::::::::::: A list of additional keywords to be used to assist searching for the distribution in a larger catalog. Example:: Keywords: dog puppy voting election Home-page (optional) :::::::::::::::::::: A string containing the URL for the distribution's home page. Example:: Home-page: http://www.example.com/~cschultz/bvote/ Download-URL (optional) ::::::::::::::::::::::: A string containing the URL from which this version of the distribution can be downloaded. (This means that the URL can't be something like ".../BeagleVote-latest.tgz", but instead must be ".../BeagleVote-0.45.tgz".) Author (optional) ::::::::::::::::: A string containing the author's name at a minimum; additional contact information may be provided. Example:: Author: C. Schultz, Universal Features Syndicate, Los Angeles, CA Author-email (optional) ::::::::::::::::::::::: A string containing the author's e-mail address. It contains a name and e-mail address in the RFC 5322 recommended ``Address Specification`` format. Example:: Author-email: "C. Schultz" Maintainer (optional) ::::::::::::::::::::: A string containing the maintainer's name at a minimum; additional contact information may be provided. Note that this field is intended for use when a project is being maintained by someone other than the original author: it should be omitted if it is identical to ``Author``. Example:: Maintainer: C. Schultz, Universal Features Syndicate, Los Angeles, CA Maintainer-email (optional) ::::::::::::::::::::::::::: A string containing the maintainer's e-mail address. It has the same format as ``Author-email``. Note that this field is intended for use when a project is being maintained by someone other than the original author: it should be omitted if it is identical to ``Author-email``. Example:: Maintainer-email: "C. Schultz" License (optional) :::::::::::::::::: Text indicating the license covering the distribution where the license is not a selection from the "License" Trove classifiers. See "Classifier" below. This field may also be used to specify a particular version of a license which is named via the ``Classifier`` field, or to indicate a variation or exception to such a license. Examples:: License: This software may only be obtained by sending the author a postcard, and then the user promises not to redistribute it. License: GPL version 3, excluding DRM provisions The full text of the license would normally be included in a separate file. Classifier (multiple use) ::::::::::::::::::::::::: Each entry is a string giving a single classification value for the distribution. Classifiers are described in PEP 301 [2]. Examples:: Classifier: Development Status :: 4 - Beta Classifier: Environment :: Console (Text Based) Requires-Dist (multiple use) :::::::::::::::::::::::::::: Each entry contains a string naming some other distutils project required by this distribution. The format of a requirement string is identical to that of a distutils project name (e.g., as found in the ``Name:`` field. optionally followed by a version declaration within parentheses. The distutils project names should correspond to names as found on the `Python Package Index`_. Version declarations must follow the rules described in `Version Specifiers`_ Examples:: Requires-Dist: pkginfo Requires-Dist: PasteDeploy Requires-Dist: zope.interface (>3.5.0) Setup-Requires-Dist (multiple use) :::::::::::::::::::::::::::::::::: Like Requires-Dist, but names dependencies needed while the distributions's distutils / packaging `setup.py` / `setup.cfg` is run. Commonly used to generate a manifest from version control. Examples:: Setup-Requires-Dist: custom_setup_command Dependencies mentioned in `Setup-Requires-Dist` may be installed exclusively for setup and are not guaranteed to be available at run time. Provides-Dist (multiple use) :::::::::::::::::::::::::::: Each entry contains a string naming a Distutils project which is contained within this distribution. This field *must* include the project identified in the ``Name`` field, followed by the version : Name (Version). A distribution may provide additional names, e.g. to indicate that multiple projects have been bundled together. For instance, source distributions of the ``ZODB`` project have historically included the ``transaction`` project, which is now available as a separate distribution. Installing such a source distribution satisfies requirements for both ``ZODB`` and ``transaction``. A distribution may also provide a "virtual" project name, which does not correspond to any separately-distributed project: such a name might be used to indicate an abstract capability which could be supplied by one of multiple projects. E.g., multiple projects might supply RDBMS bindings for use by a given ORM: each project might declare that it provides ``ORM-bindings``, allowing other projects to depend only on having at most one of them installed. A version declaration may be supplied and must follow the rules described in `Version Specifiers`_. The distribution's version number will be implied if none is specified. Examples:: Provides-Dist: OtherProject Provides-Dist: AnotherProject (3.4) Provides-Dist: virtual_package Obsoletes-Dist (multiple use) ::::::::::::::::::::::::::::: Each entry contains a string describing a distutils project's distribution which this distribution renders obsolete, meaning that the two projects should not be installed at the same time. Version declarations can be supplied. Version numbers must be in the format specified in `Version Specifiers`_. The most common use of this field will be in case a project name changes, e.g. Gorgon 2.3 gets subsumed into Torqued Python 1.0. When you install Torqued Python, the Gorgon distribution should be removed. Examples:: Obsoletes-Dist: Gorgon Obsoletes-Dist: OtherProject (<3.0) Requires-Python (optional) :::::::::::::::::::::::::: This field specifies the Python version(s) that the distribution is guaranteed to be compatible with. Version numbers must be in the format specified in `Version Specifiers`_. Examples:: Requires-Python: 2.5 Requires-Python: >2.1 Requires-Python: >=2.3.4 Requires-Python: >=2.5,<2.7 Requires-External (multiple use) :::::::::::::::::::::::::::::::: Each entry contains a string describing some dependency in the system that the distribution is to be used. This field is intended to serve as a hint to downstream project maintainers, and has no semantics which are meaningful to the ``distutils`` distribution. The format of a requirement string is a name of an external dependency, optionally followed by a version declaration within parentheses. Because they refer to non-Python software releases, version numbers for this field are **not** required to conform to the format specified in PEP 386: they should correspond to the version scheme used by the external dependency. Notice that there's is no particular rule on the strings to be used. Examples:: Requires-External: C Requires-External: libpng (>=1.5) Project-URL (multiple use) :::::::::::::::::::::::::: A string containing a label and a browsable URL for the project, separated by the last occurrence of comma and space ", ". Example:: Bug, Issue Tracker, http://bitbucket.org/tarek/distribute/issues/ The label is a free text. Provides-Extra (multiple use) ::::::::::::::::::::::::::::: A string containing the name of an optional feature. Must be printable ASCII, not containing whitespace, comma (,), or square brackets []. May be used to make a dependency conditional on whether the optional feature has been requested. Example:: Name: beaglevote Provides-Extra: pdf Requires-Dist: reportlab; extra == 'pdf' Requires-Dist: nose; extra == 'test' Requires-Dist: sphinx; extra == 'doc' A second distribution requires an optional dependency by placing it inside square brackets and can request multiple features by separating them with a comma (,). The full set of requirements is the union of the `Requires-Dist` sets evaluated with `extra` set to `None` and then to the name of each requested feature. Example:: Requires-Dist: beaglevote[pdf] -> requires beaglevote, reportlab Requires-Dist: beaglevote[test, doc] -> requires beaglevote, sphinx, nose Two feature names `test` and `doc` are reserved to mark dependencies that are needed for running automated tests and generating documentation, respectively. It is legal to specify `Provides-Extra` without referencing it in any `Requires-Dist`. It is an error to request a feature name that has not been declared with `Provides-Extra`. Extension (multiple use) :::::::::::::::::::::::: An ASCII string, not containing whitespace or the / character, that indicates the presence of extended metadata. Additional tags defined by an `Extension: Chili` must be of the form `Chili/Name`:: Extension: Chili Chili/Type: Poblano Chili/Heat: Mild An implementation might iterate over all the declared `Extension:` fields to invoke the processors for those extensions. As the order of the fields is not used, the `Extension: Chili` field may appear before or after its declared tags `Chili/Type:` etc. Version Specifiers ================== Version specifiers are a series of conditional operators and version numbers, separated by commas. Conditional operators must be one of "<", ">", "<=", ">=", "==" and "!=". Any number of conditional operators can be specified, e.g. the string ">1.0, !=1.3.4, <2.0" is a legal version declaration. The comma (",") is equivalent to the **and** operator. Each version number must be in the format specified in PEP 386. When a version is provided, it always includes all versions that starts with the same value. For example the "2.5" version of Python will include versions like "2.5.2" or "2.5.3". Pre and post releases in that case are excluded. So in our example, versions like "2.5a1" are not included when "2.5" is used. If the first version of the range is required, it has to be explicitly given. In our example, it will be "2.5.0". Notice that some projects might omit the ".0" prefix for the first release of the "2.5.x" series: - 2.5 - 2.5.1 - 2.5.2 - etc. In that case, "2.5.0" will have to be explicitly used to avoid any confusion between the "2.5" notation that represents the full range. It is a recommended practice to use schemes of the same length for a series to completely avoid this problem. Some Examples: - ``Requires-Dist: zope.interface (3.1)``: any version that starts with 3.1, excluding post or pre-releases. - ``Requires-Dist: zope.interface (==3.1)``: equivalent to ``Requires-Dist: zope.interface (3.1)``. - ``Requires-Dist: zope.interface (3.1.0)``: any version that starts with 3.1.0, excluding post or pre-releases. Since that particular project doesn't use more than 3 digits, it also means "only the 3.1.0 release". - ``Requires-Python: 3``: Any Python 3 version, no matter wich one, excluding post or pre-releases. - ``Requires-Python: >=2.6,<3``: Any version of Python 2.6 or 2.7, including post releases of 2.6, pre and post releases of 2.7. It excludes pre releases of Python 3. - ``Requires-Python: 2.6.2``: Equivalent to ">=2.6.2,<2.6.3". So this includes only Python 2.6.2. Of course, if Python was numbered with 4 digits, it would have include all versions of the 2.6.2 series. - ``Requires-Python: 2.5.0``: Equivalent to ">=2.5.0,<2.5.1". - ``Requires-Dist: zope.interface (3.1,!=3.1.3)``: any version that starts with 3.1, excluding post or pre-releases of 3.1 *and* excluding any version that starts with "3.1.3". For this particular project, this means: "any version of the 3.1 series but not 3.1.3". This is equivalent to: ">=3.1,!=3.1.3,<3.2". Environment markers =================== An **environment marker** is a marker that can be added at the end of a field after a semi-colon (";"), to add a condition about the execution environment. Here are some example of fields using such markers:: Requires-Dist: pywin32 (>1.0); sys.platform == 'win32' Obsoletes-Dist: pywin31; sys.platform == 'win32' Requires-Dist: foo (1,!=1.3); platform.machine == 'i386' Requires-Dist: bar; python_version == '2.4' or python_version == '2.5' Requires-External: libxslt; 'linux' in sys.platform The micro-language behind this is a simple subset of Python: it compares only strings, with the ``==`` and ``in`` operators (and their opposites), and with the ability to combine expressions. Parenthesis are supported for grouping. The pseudo-grammar is :: EXPR [in|==|!=|not in] EXPR [or|and] ... where ``EXPR`` belongs to any of those: - python_version = '%s.%s' % (sys.version_info[0], sys.version_info[1]) - python_full_version = sys.version.split()[0] - os.name = os.name - sys.platform = sys.platform - platform.version = platform.version() - platform.machine = platform.machine() - platform.python_implementation = platform.python_implementation() - a free string, like ``'2.4'``, or ``'win32'`` - extra = (name of requested feature) or None Notice that ``in`` is restricted to strings, meaning that it is not possible to use other sequences like tuples or lists on the right side. The fields that benefit from this marker are: - Requires-Python - Requires-External - Requires-Dist - Setup-Requires-Dist - Provides-Dist - Obsoletes-Dist - Classifier (The `extra` variable is only meaningful for Requires-Dist.) Summary of Differences From PEP 345 =================================== * Metadata-Version is now 1.3. * Values are now expected to be UTF-8. * A payload (containing the description) may appear after the headers. * Added `extra` to environment markers. * Most fields are now optional. * Changed fields: - Description - Project-URL - Requires-Dist * Added fields: - Extension - Provides-Extra - Setup-Requires-Dist References ========== This document specifies version 1.3 of the metadata format. Version 1.0 is specified in PEP 241. Version 1.1 is specified in PEP 314. Version 1.2 is specified in PEP 345. .. [1] reStructuredText markup: http://docutils.sourceforge.net/ .. _`Python Package Index`: http://pypi.python.org/pypi/ .. [2] PEP 301: http://www.python.org/dev/peps/pep-0301/ Appendix ======== Parsing and generating the Metadata 1.3 serialization format using Python 3.3:: # Metadata 1.3 demo from email.generator import Generator from email import header from email.parser import Parser from email.policy import Compat32 from email.utils import _has_surrogates class MetadataPolicy(Compat32): max_line_length = 0 continuation_whitespace = '\t' def _sanitize_header(self, name, value): if not isinstance(value, str): return value if _has_surrogates(value): raise NotImplementedError() else: return value def _fold(self, name, value, sanitize): body = ((self.linesep+self.continuation_whitespace) .join(value.splitlines())) return ''.join((name, ': ', body, self.linesep)) if __name__ == "__main__": import sys import textwrap pkg_info = """\ Metadata-Version: 1.3 Name: package Version: 0.1.0 Summary: A package. Description: Description =========== A description of the package. """ m = Parser(policy=MetadataPolicy()).parsestr(pkg_info) m['License'] = 'GPL' description = m['Description'] description_lines = description.splitlines() m.set_payload(description_lines[0] + '\n' + textwrap.dedent('\n'.join(description_lines[1:])) + '\n') del m['Description'] # Correct if sys.stdout.encoding == 'UTF-8': Generator(sys.stdout, maxheaderlen=0).flatten(m) Copyright ========= This document has been placed in the public domain. .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 End: