Standard way to embed version into Python package?

Question

Is there a standard way to associate version string with a Python package in such way that I could do the following?

import foo print(foo.version) 

I would imagine there's some way to retrieve that data without any extra hardcoding, since minor/major strings are specified in setup.py already. Alternative solution that I found was to have import __version__ in my foo/__init__.py and then have __version__.py generated by setup.py.

Answer 1

Not directly an answer to your question, but you should consider naming it __version__, not version.

This is almost a quasi-standard. Many modules in the standard library use __version__, and this is also used in lots of 3rd-party modules, so it's the quasi-standard.

Usually, __version__ is a string, but sometimes it's also a float or tuple.

Edit: as mentioned by S.Lott (Thank you!), PEP 8 says it explicitly:

Module Level Dunder Names

Module level "dunders" (i.e. names with two leading and two trailing underscores) such as __all__, __author__, __version__, etc. should be placed after the module docstring but before any import statements except from __future__ imports.

You should also make sure that the version number conforms to the format described in PEP 440 (PEP 386 a previous version of this standard).

Answer 2

I use a single _version.py file as the "once cannonical place" to store version information:

1. It provides a __version__ attribute.

2. It provides the standard metadata version. Therefore it will be detected by pkg_resources or other tools that parse the package metadata (EGG-INFO and/or PKG-INFO, PEP 0345).

3. It doesn't import your package (or anything else) when building your package, which can cause problems in some situations. (See the comments below about what problems this can cause.)

4. There is only one place that the version number is written down, so there is only one place to change it when the version number changes, and there is less chance of inconsistent versions.

Here is how it works: the "one canonical place" to store the version number is a .py file, named "_version.py" which is in your Python package, for example in myniftyapp/_version.py. This file is a Python module, but your setup.py doesn't import it! (That would defeat feature 3.) Instead your setup.py knows that the contents of this file is very simple, something like:

__version__ = "3.6.5" 

And so your setup.py opens the file and parses it, with code like:

import re VERSIONFILE="myniftyapp/_version.py" verstrline = open(VERSIONFILE, "rt").read() VSRE = r"^__version__ = ['\"]([^'\"]*)['\"]" mo = re.search(VSRE, verstrline, re.M) if mo:     verstr = mo.group(1) else:     raise RuntimeError("Unable to find version string in %s." % (VERSIONFILE,)) 

Then your setup.py passes that string as the value of the "version" argument to setup(), thus satisfying feature 2.

To satisfy feature 1, you can have your package (at run-time, not at setup time!) import the _version file from myniftyapp/__init__.py like this:

from _version import __version__ 

Here is an example of this technique that I've been using for years.

The code in that example is a bit more complicated, but the simplified example that I wrote into this comment should be a complete implementation.

Here is example code of importing the version.

If you see anything wrong with this approach, please let me know.