Use version control tags to discover version numbers

## vcversioner

Elevator pitch: you can write a setup.py with no version information specified, and vcversioner will find a recent, properly-formatted VCS tag and extract a version from it.

It’s much more convenient to be able to use your version control system’s tagging mechanism to derive a version number than to have to duplicate that information all over the place. I eventually ended up copy-pasting the same code into a couple different setup.py files just to avoid duplicating version information. But, copy-pasting is dumb and unit testing setup.py files is hard. This code got factored out into vcversioner.

### Basic usage

vcversioner installs itself as a setuptools hook, which makes its use exceedingly simple:

from setuptools import setup

setup(
# [...]
setup_requires=['vcversioner'],
vcversioner={},
)

The presence of a vcversioner argument automagically activates vcversioner and updates the project’s version. The parameter to the vcversioner argument can also be a dict of keyword arguments which find_version will be called with.

To allow tarballs to be distributed without requiring a .git (or .hg, etc.) directory, vcversioner will also write out a file named (by default) version.txt. Then, if there is no VCS program or the program is unable to find any version information, vcversioner will read version information from the version.txt file. However, this file needs to be included in a distributed tarball, so the following line should be added to MANIFEST.in:

include version.txt

This isn’t necessary if setup.py will always be run from a checkout, but otherwise is essential for vcversioner to know what version to use.

The name version.txt also can be changed by specifying the version_file parameter. For example:

from setuptools import setup

setup(
# [...]
setup_requires=['vcversioner'],
vcversioner={
'version_file': 'custom_version.txt',
},
)

For compatibility with semantic versioning, vcversioner will strip leading 'v's from version tags. That is, the tag v1.0 will be treated as if it was 1.0.

Other prefixes can be specified to be stripped by using the strip_prefix argument to vcversioner. For compatibility with git-dch, one could specify the strip_prefix as 'debian/'.

### Non-hook usage

It’s not necessary to depend on vcversioner; while pip will take care of dependencies automatically, sometimes having a self-contained project is simpler. vcversioner is a single file which is easy to add to a project. Simply copy the entire vcversioner.py file adjacent to the existing setup.py file and update the usage slightly:

from setuptools import setup
import vcversioner

setup(
# [...]
version=vcversioner.find_version().version,
)

This is necessary because the vcversioner distutils hook won’t be available.

### Version modules

setup.py isn’t the only place that version information gets duplicated. By generating a version module, the __init__.py file of a package can import version information. For example, with a package named spam:

from setuptools import setup

setup(
# [...]
setup_requires=['vcversioner'],
vcversioner={
'version_module_paths': ['spam/_version.py'],
},
)

This will generate a spam/_version.py file that defines __version__ and __revision__. Then, in spam/__init__.py:

from spam._version import __version__, __revision__

Since this acts like (and is) a regular python module, changing MANIFEST.in is not required.

### Customizing VCS commands

vcversioner by default tries to detect which VCS is being used and picks a command to run based on that. For git, that is git --git-dir %(root)s/.git describe --tags --long. For hg, that is hg log -R %(root)s -r . --template '{latesttag}-{latesttagdistance}-hg{node|short}'.

Any command should output a string that describes the current commit in the format 1.0-0-gdeadbeef. Specifically, that is <version number>-<number of commits between the current commit and the version tagged commit>-<revision>. The revision should have a VCS-specific prefix, e.g. g for git and hg for hg.

However, sometimes this isn’t sufficient. If someone wanted to only use annotated tags, the git command could be amended like so:

from setuptools import setup

setup(
# [...]
setup_requires=['vcversioner'],
vcversioner={
'vcs_args': ['git', 'describe', '--long'],
},
)

The vcs_args parameter must always be a list of strings, which will not be interpreted by the shell. This is the same as what subprocess.Popen expects.

This argument used to be spelled git_args until support for multiple VCS systems was added.

### Development versions

vcversioner can also automatically make a version that corresponds to a commit that isn’t itself tagged. Following PEP 386, this is done by adding a .post suffix to the version specified by a tag on an earlier commit. For example, if the current commit is three revisions past the 1.0 tag, the computed version will be 1.0.post3.

This behavior can be disabled by setting the include_dev_version parameter to False. In that case, the aforementioned untagged commit’s version would be just 1.0.

Since hg requires a commit to make a tag, there’s a parameter decrement_dev_version to subtract one from the number of commits after the most recent tag. If the VCS used is detected to be hg (i.e. the revision starts with 'hg') and decrement_dev_version is not specified as False, decrement_dev_version will be automatically set to True.

### Project roots

In order to prevent contamination from other source repositories, vcversioner in the 1.x version series will only look in the project root directory for repositories. The project root defaults to the current working directory, which is often the case when running setup.py. This can be changed by specifying the root parameter. Someone concerned with being able to run setup.py from directories other than the directory containing setup.py should determine the project root from __file__ in setup.py:

from setuptools import setup
import os

setup(
# [...]
setup_requires=['vcversioner'],
vcversioner={
'root': os.path.dirname(os.path.abspath(__file__)),
},
)

To get the same behavior in the 0.x version series, vcs_args can be set to include the --git-dir flag:

from setuptools import setup

setup(
# [...]
setup_requires=['vcversioner'],
vcversioner={
vcs_args=['git', '--git-dir', '%(root)s/.git', 'describe',
'--tags', '--long'],
},
)

By default, version.txt is also read from the project root.

#### Substitutions

As seen above, root, version_file, and vcs_args each support some substitutions:

%(root)s

The value provided for root. This is not available for the root parameter itself.

%(pwd)s

The current working directory.

/ will automatically be translated into the correct path separator for the current platform, such as : or \.

### Sphinx documentation

Sphinx documentation is yet another place where version numbers get duplicated. Fortunately, since sphinx configuration is python code, vcversioner can be used there too. Assuming vcversioner is installed system-wide, this is quite easy. Since Sphinx is typically run with the current working directory as <your project root>/docs, it’s necessary to tell vcversioner where the project root is. Simply change your conf.py to include:

import vcversioner
version = release = vcversioner.find_version(root='..').version

This assumes that your project root is the parent directory of the current working directory. A slightly longer version which is a little more robust would be:

import vcversioner, os
version = release = vcversioner.find_version(
root=os.path.dirname(os.path.dirname(os.path.abspath(__file__)))).version

This version is more robust because it finds the project root not relative to the current working directory but instead relative to the conf.py file.

If vcversioner is bundled with your project instead of relying on it being installed, you might have to add the following to your conf.py before import vcversioner:

import sys, os
sys.path.insert(0, os.path.abspath('..'))

This line, or something with the same effect, is sometimes already present when using the sphinx autodoc extension.

Using vcversioner is even possible when building documentation on Read the Docs. If vcversioner is bundled with your project, nothing further needs to be done. Otherwise, you need to tell Read the Docs to install vcversioner before it builds the documentation. This means using a requirements.txt file.

If your project is already set up to install dependencies with a requirements.txt file, add vcversioner to it. Otherwise, create a requirements.txt file. Assuming your documentation is in a docs subdirectory of the main project directory, create docs/requirements.txt containing a vcversioner line.

Then, make the following changes to your project’s configuration: (Project configuration is edited at e.g. https://readthedocs.org/dashboard/vcversioner/edit/)

• Check the checkbox under Use virtualenv.

• If there was no requirements.txt previously, set the Requirements file to the newly-created one, e.g. docs/requirements.txt.

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