An updated draft of PEP 426 has been posted. Based on the feedback received on the previous draft, I decided that the PEP needed to provide substantially more guidance to readers on what the different components of the versioning scheme *meant*, rather than assuming that the reader would be able to figure out for themselves which parts were relevant for new projects and which parts were only included for consistency with the development practices of some established projects. There are only a couple of actual *changes* in this version of the specification that may affect implementations: - single-component release numbers are now permitted, which makes it substantially easier to refer to an entire release series in a version specifier. - the "order by metadata version" idea has been dropped, as Daniel Holth pointed out off-list that some metadata generation tools may follow the model of setting the Metadata Version to the lowest version which contains all of the required fields. That's a good mechanism for maximising interoperability, so I removed the idea of requiring that the metadata version never go backwards. The in-depth explanation of the version scheme, along with the rationale for the various changes, does mean that the spec has now grown to almost 3 times the size of PEP 345 and 5 times the size of PEP 314. However, I think metadata interoperability is an area where being overly terse in the past has been a major cause of problems, so I'm definitely inclined to err on the side of too much information, rather than too little. Web version: http://www.python.org/dev/peps/pep-0426/ Regards, Nick. =================================== PEP: 426 Title: Metadata for Python Software Packages 1.3 Version: $Revision$ Last-Modified: $Date$ Author: Daniel Holth , Donald Stufft , Nick Coghlan Discussions-To: Distutils SIG Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 30 Aug 2012 Post-History: 14 Nov 2012, 5 Feb 2013, 7 Feb 2013, 9 Feb 2013 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. It also adds support for optional features of distributions and allows the description to be placed into a payload section. Finally, this version addresses several issues with the previous iteration of the standard version identification scheme. 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 case-insensitive keys and no maximum line length, optionally followed by a blank line and a payload containing a description of the distribution. This format 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. Metadata header fields ======================= This section specifies the names and semantics of each of the supported fields in the metadata header. 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 header section of 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 identifier. See `Version scheme`_ below. Example:: Version: 1.0a2 Summary ------- A one-line summary of what the distribution does. Example:: Summary: A module for collecting votes from beagles. Description (optional, deprecated) ---------------------------------- Starting with 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. See `Describing the Distribution`_ for more information on the expected contents of this field. Since a line separator immediately followed by another line separator indicates the end of the headers section, any line separators in a ``Description`` header field must be suffixed by whitespace to indicate continuation. It is an error to provide both a ``Description`` header and a metadata payload. Keywords (optional) ------------------- A list of additional whitespace separated 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".) 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 ", ". The label consists of any permitted header text, including commas. Example:: Bug, Issue Tracker, http://bitbucket.org/tarek/distribute/issues/ 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) Provides-Dist (multiple use) ---------------------------- Each entry contains a string naming a requirement that is satisfied by installing this distribution. These strings must be of the form ``Name`` or ``Name (Version)``, following the formats of the corresponding field definitions. For ease of metadata consumption, distributions are required to explicitly include a ``Provides-Dist`` entry for their own name and version. This also allows developers of a project to discourage users explicitly depending on the project (by deliberately omitting this entry). A distribution may provide additional names, e.g. to indicate that multiple projects have been merged into and replaced by a single distribution or to indicate that this project is a substitute for another. For instance, distribute (a fork of setuptools) can include a ``Provides-Dist: setuptools`` entry to prevent the conflicting package from being downloaded and installed when distribute is already installed. A distribution that has been merged with another might ``Provides-Dist`` the obsolete name(s) to satisfy any projects that require the obsolete distribution's name. 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 ``ExampleORM-somedb-bindings``, allowing other projects to depend only on having at least one of them installed. A version declaration may be supplied and must follow the rules described in `Version scheme`_. The distribution's version identifier will be implied if none is specified. Examples:: Provides-Dist: ThisProject Provides-Dist: AnotherProject (3.4) Provides-Dist: virtual_package 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. See `Optional Features`_ for details on the use of this field. Example:: Name: beaglevote Provides-Extra: pdf Requires-Dist: reportlab; extra == 'pdf' Requires-Dist: nose; extra == 'test' Requires-Dist: sphinx; extra == 'doc' Obsoleted-By (optional) ----------------------- Indicates that this project is no longer being developed. The named project provides a substitute or replacement. A version declaration may be supplied and must follow the rules described in `Version specifiers`_. Possible uses for this field include handling project name changes and project mergers. Examples:: Name: BadName Obsoleted-By: AcceptableName Name: SeparateProject Obsoleted-By: MergedProject (>=4.0.0) 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 distribution name (e.g., as found in the ``Name:`` field) optionally followed by a version declaration within parentheses. The distribution names should correspond to names as found on the `Python Package Index`_; often the same as, but distinct from, the module names as accessed with ``import x``. Version declarations must follow the rules described in `Version specifiers`_ Distributions may also depend on optional features of other distributions. See `Optional Features`_ for details. Examples:: Requires-Dist: pkginfo Requires-Dist: PasteDeploy Requires-Dist: zope.interface (>3.5.0) Dependencies mentioned in ``Requires-Dist`` may be installed exclusively at run time and are not guaranteed to be available when creating or installing a package. If a dependency is needed during distribution creation or installation *and* at run time, it should be listed under both ``Requires-Dist`` and ``Setup-Requires-Dist``. Setup-Requires-Dist (multiple use) ---------------------------------- Like ``Requires-Dist``, but names dependencies needed in order to build, package or install the distribution. Commonly used to bring in extra compiler support or a package needed to generate a manifest from version control. Distributions may also depend on optional features of other distributions. See `Optional Features`_ for details. 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. If a dependency is needed during distribution creation or installation *and* at run time, it should be listed under both ``Requires-Dist`` and ``Setup-Requires-Dist``. Requires-Python (multiple use) ------------------------------ This field specifies the Python version(s) that the distribution is guaranteed to be compatible with. Version declarations must be in the format specified in `Version specifiers`_. Examples:: Requires-Python: 3.2 Requires-Python: >3.1 Requires-Python: >=2.3.4 Requires-Python: >=2.5,<2.7 If specified multiple times, the Python version must satisfy all such constraints to be considered compatible. This is most useful in combination with appropriate `Environment markers`_. For example, if a feature was initially introduced to Python as a Unix-specific addition, and then Windows support was added in the subsequent release, this could be indicated with the following pair of entries:: Requires-Python: >= 3.1 Requires-Python: >= 3.2; sys.platform == 'win32' 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 identifiers for this field are **not** required to conform to the format described in `Version scheme`_: they should correspond to the version scheme used by the external dependency. Notice that there is no particular rule on the strings to be used. Examples:: Requires-External: C Requires-External: libpng (>=1.5) 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`__ above. __ `Classifier (multiple use)`_ 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 Extension (multiple use) ------------------------ An ASCII string, not containing whitespace or the ``/`` character, that indicates the presence of extended metadata. The additional fields defined by the extension are then prefixed with the name of the extension and the ``/`` character. For example:: Extension: Chili Chili/Type: Poblano Chili/Heat: Mild To avoid name conflicts, it is recommended that distribution names be used to identify metadata extensions. This practice will also make it easier to find authoritative documentation for metadata extensions. As the order of the metadata headers is not constrained, the ``Extension: Chili`` field may appear before or after the corresponding extension fields ``Chili/Type:`` etc. Values in extension fields must still respect the general formatting requirements for metadata headers. A bare ``Extension: Name`` entry with no corresponding extension fields is permitted. It may, for example, indicate the expected presence of an additional metadata file rather than the presence of extension fields. An extension field with no corresponding ``Extension: Name`` entry is an error. Describing the distribution =========================== The distribution metadata should include a longer description of the distribution that may run to several paragraphs. Software that deals with metadata should not assume any maximum size for the description. The recommended location for the description is in the metadata payload, separated from the header fields by at least one completely blank line (that is, two successive line separators with no other characters between them, not even whitespace). Alternatively, the description may be provided in the `Description`__ metadata header field. Providing both a ``Description`` field and a payload is an error. __ `Description (optional, deprecated)`_ The distribution description can be written using reStructuredText markup [1]_. For programs that work with the metadata, supporting markup is optional; programs may also display the contents of the field as plain text without any special formatting. This means that authors should be conservative in the markup they use. Version scheme ============== Version identifiers must comply with the following scheme:: N[.N]+[{a|b|c|rc}N][.postN][.devN] Version identifiers which do not comply with this scheme are an error. Projects which wish to use non-compliant version identifiers must restrict themselves to metadata v1.1 (PEP 314) or earlier, as those specifications do not constrain the versioning scheme. Any given version will be a "release", "pre-release", "post-release" or "developmental release" as defined in the following sections. .. note:: Some hard to read version identifiers are permitted by this scheme in order to better accommodate the wide range of versioning practices across existing public and private Python projects. Accordingly, some of the versioning practices which are technically permitted by the PEP are strongly discouraged for new projects. Where this is the case, the relevant details are noted in the following sections. Releases -------- A release number is a version identifier that consists solely of one or more non-negative integer values, separated by dots:: N[.N]+ Releases within a project must be numbered in a consistently increasing fashion. Ordering considers the numeric value of each component in turn, with "component does not exist" sorted ahead of all numeric values. While any number of additional components after the first are permitted under this scheme, the most common variants are to use two components ("major.minor") or three components ("major.minor.micro"). For example:: 0.9 0.9.1 0.9.2 ... 0.9.10 0.9.11 1.0 1.0.1 1.1 2.0 2.0.1 A release series is any set of release numbers that start with a common prefix. For example, ``3.3.1``, ``3.3.5`` and ``3.3.9.45`` are all part of the ``3.3`` release series. .. note:: Using both ``X.Y`` and ``X.Y.0`` as distinct release numbers within the scope of a single release series is strongly discouraged, as it makes the version ordering ambiguous for human readers. Automated tools should either treat this case as an error, or else interpret an ``X.Y.0`` release as coming *after* the corresponding ``X.Y`` release. The recommended practice is to always use release numbers of a consistent length (that is, always include the trailing ``.0``). An acceptable alternative is to consistently omit the trailing ``.0``. The example above shows both styles, always including the ``.0`` at the second level and consistently omitting it at the third level. .. note:: While date based release numbers, using the forms ``year.month`` or ``year.month.day``, are technically compliant with this scheme, their use is strongly discouraged as they can hinder automatic translation to other versioning schemes. In particular, they are completely incompatible with semantic versioning. Semantic versioning ------------------- `Semantic versioning`_ is a popular version identification scheme that is more prescriptive than this PEP regarding the significance of different elements of a release number. Even if a project chooses not to abide by the details of semantic versioning, the scheme is worth understanding as it covers many of the issues that can arise when depending on other distributions, and when publishing a distribution that others rely on. The "Major.Minor.Patch" (described in this PEP as "major.minor.micro") aspects of semantic versioning (clauses 1-9 in the 2.0.0-rc-1 specification) are fully compatible with the version scheme defined in this PEP, and abiding by these aspects is encouraged. Semantic versions containing a hyphen (pre-releases - clause 10) or a plus sign (builds - clause 11) are *not* compatible with this PEP and are not permitted in compliant metadata. Use this PEP's deliberately more restricted pre-release and developmental release notation instead. .. _Semantic versioning: http://semver.org/ Pre-releases ------------ Some projects use an "alpha, beta, release candidate" pre-release cycle to support testing by their users prior to a full release. If used as part of a project's development cycle, these pre-releases are indicated by a suffix appended directly to the last component of the release number:: X.YaN # Alpha release X.YbN # Beta release X.YcN # Release candidate (alternative notation: X.YrcN) X.Y # Full release The pre-release suffix consists of an alphabetical identifier for the pre-release phase, along with a non-negative integer value. Pre-releases for a given release are ordered first by phase (alpha, beta, release candidate) and then by the numerical component within that phase. .. note:: Using both ``c`` and ``rc`` to identify release candidates within the scope of a single release is strongly discouraged, as it makes the version ordering ambiguous for human readers. Automated tools should either treat this case as an error, or else interpret all ``rc`` versions as coming after all ``c`` versions (that is, ``rc1`` indicates a later version than ``c2``). Post-releases ------------- Some projects use post-releases to address minor errors in a release that do not affect the distributed software (for example, correcting an error in the release notes). If used as part of a project's development cycle, these post-releases are indicated by a suffix appended directly to the last component of the release number:: X.Y.postN # Post-release The post-release suffix consists of the string ``.post``, followed by a non-negative integer value. Post-releases are ordered by their numerical component, immediately following the corresponding release, and ahead of any subsequent release. .. note:: The use of post-releases to publish maintenance releases containing actual bug fixes is strongly discouraged. In general, it is better to use a longer release number and increment the final component for each maintenance release. Post-releases are also permitted for pre-releases:: X.YaN.postM # Post-release of an alpha release X.YbN.postM # Post-release of a beta release X.YcN.postM # Post-release of a release candidate .. note:: Creating post-releases of pre-releases is strongly discouraged, as it makes the version identifier difficult to parse for human readers. In general, it is substantially clearer to simply create a new pre-release by incrementing the numeric component. Developmental releases ---------------------- Some projects make regular developmental releases, and system packagers (especially for Linux distributions) may wish to create early releases which do not conflict with later project releases. If used as part of a project's development cycle, these developmental releases are indicated by a suffix appended directly to the last component of the release number:: X.Y.devN # Developmental release The developmental release suffix consists of the string ``.dev``, followed by a non-negative integer value. Developmental releases are ordered by their numerical component, immediately before the corresponding release (and before any pre-releases), and following any previous release. Developmental releases are also permitted for pre-releases and post-releases:: X.YaN.devM # Developmental release of an alpha release X.YbN.devM # Developmental release of a beta release X.YcN.devM # Developmental release of a release candidate X.Y.postN.devM # Developmental release of a post-release .. note:: Creating developmental releases of pre-releases is strongly discouraged, as it makes the version identifier difficult to parse for human readers. In general, it is substantially clearer to simply create additional pre-releases by incrementing the numeric component. Developmental releases of post-releases are also strongly discouraged, but they may be appropriate for projects which use the post-release notation for full maintenance releases which may include code changes. Examples of compliant version schemes ------------------------------------- The standard version scheme is designed to encompass a wide range of identification practices across public and private Python projects. In practice, a single project attempting to use the full flexibility offered by the scheme would create a situation where human users had difficulty figuring out the relative order of versions, even though the rules above ensure all compliant tools will order them consistently. The following examples illustrate a small selection of the different approaches projects may choose to identify their releases, while still ensuring that the "latest release" and the "latest stable release" can be easily determined, both by human users and automated tools. Simple "major.minor" versioning:: 0.1 0.2 0.3 1.0 1.1 ... Simple "major.minor.micro" versioning:: 1.1.0 1.1.1 1.1.2 1.2.0 ... "major.minor" versioning with alpha, beta and release candidate pre-releases:: 0.9 1.0a1 1.0a2 1.0b1 1.0c1 1.0 1.1a1 ... "major.minor" versioning with developmental releases, release candidates and post-releases for minor corrections:: 0.9 1.0.dev1 1.0.dev2 1.0.dev3 1.0.dev4 1.0rc1 1.0rc2 1.0 1.0.post1 1.1.dev1 ... Summary of permitted suffixes and relative ordering --------------------------------------------------- .. note:: This section is intended primarily for authors of tools that automatically process distribution metadata, rather than authors of Python distributions deciding on a versioning scheme. The numeric release component of version identifiers should be sorted in the same order as Python's tuple sorting when the release number is parsed as follows:: tuple(map(int, release_number.split("."))) Within a numeric release (``1.0``, ``2.7.3``), the following suffixes are permitted and are ordered as shown:: .devN, aN, bN, cN, rcN, <no suffix>, .postN Note that `rc` will always sort after `c` (regardless of the numeric component) although they are semantically equivalent. Tools are free to reject this case as ambiguous and remain in compliance with the PEP. Within an alpha (``1.0a1``), beta (``1.0b1``), or release candidate (``1.0c1``, ``1.0rc1``), the following suffixes are permitted and are ordered as shown:: .devN, <no suffix>, .postN Within a post-release (``1.0.post1``), the following suffixes are permitted and are ordered as shown:: devN, <no suffix> Note that ``devN`` and ``postN`` must always be preceded by a dot, even when used immediately following a numeric version (e.g. ``1.0.dev456``, ``1.0.post1``). Within a given suffix, ordering is by the value of the numeric component. The following example covers many of the possible combinations:: 1.0.dev456 1.0a1 1.0a2.dev456 1.0a12.dev456 1.0a12 1.0b1.dev456 1.0b2 1.0b2.post345.dev456 1.0b2.post345 1.0c1.dev456 1.0c1 1.0 1.0.post456.dev34 1.0.post456 1.1.dev1 Version ordering across different metadata versions --------------------------------------------------- Metadata v1.0 (PEP 241) and metadata v1.1 (PEP 314) do not specify a standard version identification or ordering scheme. This PEP does not mandate any particular approach to handling such versions, but acknowledges that the de facto standard for ordering them is the scheme used by the ``pkg_resources`` component of ``setuptools``. Software that automatically processes distribution metadata may either treat non-compliant version identifiers as an error, or attempt to normalize them to the standard scheme. This means that projects using non-compliant version identifiers may not be handled consistently across different tools, even when correctly publishing the earlier metadata versions. Package developers can help ensure consistent automated handling by marking non-compliant versions as "hidden" on the Python Package Index (removing them is generally undesirable, as users may be depending on those specific versions being available). Package users may also wish to remove non-compliant versions from any private package indexes they control. For metadata v1.2 (PEP 345), the version ordering described in this PEP should be used in preference to the one defined in PEP 386. Version specifiers ================== A version specifier consists of a series of version clauses, separated by commas. Each version clause consists of an optional comparison operator followed by a version identifier. For example:: 0.9, >= 1.0, != 1.3.4, < 2.0 Each version identifier must be in the standard format described in `Version scheme`_. The comma (",") is equivalent to a logical **and** operator. Comparison operators must be one of ``<``, ``>``, ``<=``, ``>=``, ``==`` or ``!=``. The ``==`` and ``!=`` operators are strict - in order to match, the version supplied must exactly match the specified version, with no additional trailing suffix. However, when no comparison operator is provided along with a version identifier ``V``, it is equivalent to using the following pair of version clauses:: >= V, < V+1 where ``V+1`` is the next version after ``V``, as determined by incrementing the last numeric component in ``V`` (for example, if ``V == 1.0a3``, then ``V+1 == 1.0a4``, while if ``V == 1.0``, then ``V+1 == 1.1``). This approach makes it easy to depend on a particular release series simply by naming it in a version specifier, without requiring any additional annotation. For example, the following pairs of version specifiers are equivalent:: 2 >= 2, < 3 3.3 >= 3.3, < 3.4 Whitespace between a conditional operator and the following version identifier is optional, as is the whitespace around the commas. Pre-releases of any kind, including developmental releases, are implicitly excluded from all version specifiers, *unless* a pre-release or developmental developmental release is explicitly mentioned in one of the clauses. For example, this specifier implicitly excludes all pre-releases and development releases of later versions:: >= 1.0 While these specifiers would include them:: >= 1.0a1 >= 1.0c1 >= 1.0, != 1.0b2 >= 1.0, < 2.0.dev123 Dependency resolution tools should use the above rules by default, but should also allow users to request the following alternative behaviours: * accept already installed pre-releases for all version specifiers * retrieve and install available pre-releases for all version specifiers Dependency resolution tools may also allow the above behaviour to be controlled on a per-distribution basis. Post-releases and purely numeric releases receive no special treatment - they are always included unless explicitly excluded. Given the above rules, projects which include the ``.0`` suffix for the first release in a series, such as ``2.5.0``, can easily refer specifically to that version with the clause ``2.5.0``, while the clause ``2.5`` refers to that entire series. Projects which omit the ".0" suffix for the first release of a series, by using a version string like ``2.5`` rather than ``2.5.0``, will need to use an explicit clause like ``>= 2.5, < 2.5.1`` to refer specifically to that initial release. Some examples: * ``Requires-Dist: zope.interface (3.1)``: any version that starts with 3.1, excluding 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 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, excluding pre-releases. * ``Requires-Python: >=2.6,<3``: Any version of Python 2.6 or 2.7, including post-releases (if they were used for Python). 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 include all versions of the 2.6.2 series, excluding pre-releases. * ``Requires-Python: 2.5``: Equivalent to ">=2.5,<2.6". * ``Requires-Dist: zope.interface (3.1,!=3.1.3)``: any version that starts with 3.1, excluding 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". * ``Requires-Python: >=3.3a1``: Any version of Python 3.3+, including pre-releases like 3.4a1. Depending on distributions that use non-compliant version schemes ----------------------------------------------------------------- A distribution using this version of the metadata standard may need to depend on another distribution using an earlier version of the metadata standard and a non-compliant versioning scheme. The normal ``Requires-Dist`` and ``Setup-Requires-Dist`` fields can be used for such dependencies, so long as the dependency itself can be expressed using a compliant version specifier. For more exotic dependencies, a metadata extension would be needed in order to express the dependencies accurately while still obeying the restrictions on standard version specifiers. The ``Requires-External`` field may also be used, but would not be as amenable to automatic processing. 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' 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. Parentheses are supported for grouping. The pseudo-grammar is :: EXPR [in|==|!=|not in] EXPR [or|and] ... where ``EXPR`` belongs to any of these: - 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`` - ``Classifier`` Optional features ================= Distributions may use the ``Provides-Extra`` field to declare additional features that they provide. Environment markers may then be used to indicate that particular dependencies (as specified in ``Requires-Dist`` or ``Setup-Requires-Dist``) are needed only when a particular optional feature has been requested. Other distributions then require an optional feature by placing it inside square brackets after the distribution name when declaring the dependency. Multiple features can be requisted by separating them with a comma within the brackets. The full set of dependency requirements is then the union of the sets created by first evaluating the `Requires-Dist` (or `Setup-Requires-Dist`) fields with `extra` set to `None` and then to the name of each requested feature. Example:: Requires-Dist: beaglevote[pdf] -> requires beaglevote, reportlab at run time Setup-Requires-Dist: beaglevote[test, doc] -> requires beaglevote, sphinx, nose at setup time 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`. The following feature names are implicitly defined for all distributions: - `test`: dependencies that are needed in order to run automated tests - `doc`: dependencies that are needed in order to generate documentation Listing these implicit features explicitly in a ``Provides-Extra`` field is permitted, but not required. Updating the metadata specification =================================== The metadata specification may be updated with clarifications without requiring a new PEP or a change to the metadata version. Adding new features (other than through the extension mechanism), or changing the meaning of existing fields, requires a new metadata version defined in a new PEP. Summary of differences from \PEP 345 ==================================== * Metadata-Version is now 1.3 * Most fields are now optional * Explicit permission for in-place clarifications without releasing a new version of the specification * General reformatting of the PEP to make it easier to read * Values are now expected to be UTF-8 * Changed the version scheme (eliminating the dependency on PEP 386) * Changed interpretation of version specifiers * Explicit handling of ordering and dependencies across metadata versions * Support for packaging, build and installation dependencies * the new ``Setup-Requires-Dist`` field * Optional feature mechanism * the new ``Provides-Extra`` field * ``extra`` expression defined for environment markers. * optional feature support in ``Requires-Dist`` and ``Setup-Requires-Dist`` * Metadata extension mechanism * the new ``Extension`` field and extension specific fields * Updated obsolescence mechanism * the new ``Obsoleted-By`` field * the ``Obsoletes-Dist`` field has been removed * Simpler description format * the ``Description`` field is now deprecated * A payload (containing the description) may appear after the headers. * Other changed fields: - ``Requires-Python`` (explicitly flagged as multiple use) - ``Project-URL`` (commas permitted in labels) * Clarified fields: - ``Provides-Dist`` - ``Keywords`` The rationale for major changes is given in the following sections. Standard encoding and other format clarifications ------------------------------------------------- Several aspects of the file format, including the expected file encoding, were underspecified in previous versions of the metadata standard. To make it easier to develop interoperable tools, these details are now explicitly specified. Changing the version scheme --------------------------- The key change in the version scheme in this PEP relative to that in PEP 386 is to sort top level developmental releases like ``X.Y.devN`` ahead of alpha releases like ``X.Ya1``. This is a far more logical sort order, as projects already using both development releases and alphas/betas/release candidates do not want their developmental releases sorted in between their release candidates and their full releases. There is no rationale for using ``dev`` releases in that position rather than merely creating additional release candidates. The updated sort order also means the sorting of ``dev`` versions is now consistent between the metadata standard and the pre-existing behaviour of ``pkg_resources`` (and hence the behaviour of current installation tools). Making this change should make it easier for affected existing projects to migrate to the latest version of the metadata standard. Another change to the version scheme is to allow single number versions, similar to those used by non-Python projects like Mozilla Firefox, Google Chrome and the Fedora Linux distribution. This is actually expected to be more useful for version specifiers (allowing things like the simple ``Requires-Python: 3`` rather than the more convoluted ``Requires-Python: >= 3.0, < 4``), but it is easier to allow it for both version specifiers and release numbers, rather than splitting the two definitions. Finally, as the version scheme in use is dependent on the metadata version, it was deemed simpler to merge the scheme definition directly into this PEP rather than continuing to maintain it as a separate PEP. This will also allow all of the distutils-specific elements of PEP 386 to finally be formally rejected. A more opinionated description of the versioning scheme ------------------------------------------------------- As in PEP 386, the primary focus is on codifying existing practices to make them more amenable to automation, rather than demanding that existing projects make non-trivial changes to their workflow. However, the standard scheme allows significantly more flexibility than is needed for the vast majority of simple Python packages (which often don't even need maintenance releases - many users are happy with needing to upgrade to a new feature release to get bug fixes). For the benefit of novice developers, and for experienced developers wishing to better understand the various use cases, the specification now goes into much greater detail on the components of the defined version scheme, including examples of how each component may be used in practice. The PEP also explicitly guides developers in the direction of semantic versioning (without requiring it), and discourages the use of several aspects of the full versioning scheme that have largely been included in order to cover esoteric corner cases in the practices of existing projects and in repackaging software for Linux distributions. Changing the interpretation of version specifiers ------------------------------------------------- The previous interpretation of version specifiers made it very easy to accidentally download a pre-release version of a dependency. This in turn made it difficult for developers to publish pre-release versions of software to the Python Package Index, as leaving the package set as public would lead to users inadvertently downloading pre-release software, while hiding it would defeat the purpose of publishing it for user testing. The previous interpretation also excluded post-releases from some version specifiers for no adequately justified reason. The updated interpretation is intended to make it difficult to accidentally accept a pre-release version as satisfying a dependency, while allowing pre-release versions to be explicitly requested when needed. Packaging and build and installation dependencies ------------------------------------------------- The new ``Setup-Requires-Dist`` field allows a distribution to indicate when a dependency is needed to package, build or install the distribution, rather than being needed to run the software after installation. This should allow distribution tools to effectively support a wider range of distribution requirements. Support for optional features of distributions ---------------------------------------------- The new ``Provides-Extra`` field allows distributions to declare optional features, and to use environment markers to reduce their dependencies when those features are not requested. Environment markers may also be used to require a later version of Python when particular features are requested. The ``Requires-Dist`` and ``Setup-Requires-Dist`` fields then allow distributions to require optional features of other distributions. The ``test`` and ``doc`` features are implicitly defined for all distributions, as one key motivation for this feature is to encourage distributions to explicitly declare the dependencies needed to run their automatic tests, or build their documentation, without demanding those dependencies be present in order to merely install or use the software. Support for metadata extensions ------------------------------- The new ``Extension`` field effectively allows sections of the metadata namespace to be delegated to other distributions, while preserving a standard overal format metadata format for easy of processing by distribution tools that do not support a particular extension. It also works well in combination with the new ``Setup-Requires-Dist`` field to allow a distribution to depend on tools which *do* know how to handle the chosen extension, and the new optional features mechanism, allowing support for particular extensions to be provided as optional features. Updated obsolescence mechanism ------------------------------ The marker to indicate when a project is obsolete and should be replaced has been moved to the obsolete project (the new ``Obsoleted-By`` field), replacing the previous marker on the replacement project (the removed ``Obsoletes-Dist`` field). This should allow distribution tools to more easily warn users of obsolete projects and their suggested replacements. The ``Obsoletes-Dist`` header is removed rather than deprecated as it is not widely supported, and so removing it does not present any significant barrier to tools and projects adopting the new metadata format. Simpler description format -------------------------- Distribution descriptions are often quite long, sometimes including a short guide to using the module. Moving them into the file payload allows them to be formatted neatly as reStructuredText without needing to carefully avoid the introduction of a blank line that would terminate the header section. The ``Description`` header is deprecated rather than removed to support easier conversion of existing tools and projects to the new metadata format. 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. The initial attempt at a standardised version scheme, along with the justifications for needing such a standard can be found in PEP 386. .. [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. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia