What is the best project structure for a Python ap

Question

Imagine that you want to develop a non-trivial end-user desktop (not web) application in Python. What is the best way to structure the project's folder hierarchy?

Desirable features are ease of maintenance, IDE-friendliness, suitability for source control branching/merging, and easy generation of install packages.

In particular:

1. Where do you put the source?
2. Where do you put application startup scripts?
3. Where do you put the IDE project cruft?
4. Where do you put the unit/acceptance tests?
5. Where do you put non-Python data such as config files?
6. Where do you put non-Python sources such as C++ for pyd/so binary extension modules?

Answer 1

Check out Open Sourcing a Python Project the Right Way.

Let me excerpt the project layout part of that excellent article:

When setting up a project, the layout (or directory structure) is important to get right. A sensible layout means that potential contributors don't have to spend forever hunting for a piece of code; file locations are intuitive. Since we're dealing with an existing project, it means you'll probably need to move some stuff around.

Let's start at the top. Most projects have a number of top-level files (like setup.py, README.md, requirements.txt, etc). There are then three directories that every project should have:

• A docs directory containing project documentation
• A directory named with the project's name which stores the actual Python package
• A test directory in one of two places
  • Under the package directory containing test code and resources
  • As a stand-alone top level directory To get a better sense of how your files should be organized, here's a simplified snapshot of the layout for one of my projects, sandman:

$ pwd
~/code/sandman
$ tree
.
|- LICENSE
|- README.md
|- TODO.md
|- docs
|   |-- conf.py
|   |-- generated
|   |-- index.rst
|   |-- installation.rst
|   |-- modules.rst
|   |-- quickstart.rst
|   |-- sandman.rst
|- requirements.txt
|- sandman
|   |-- __init__.py
|   |-- exception.py
|   |-- model.py
|   |-- sandman.py
|   |-- test
|       |-- models.py
|       |-- test_sandman.py
|- setup.py

As you can see, there are some top level files, a docs directory (generated is an empty directory where sphinx will put the generated documentation), a sandman directory, and a test directory under sandman.

Answer 2

Doesn't too much matter. Whatever makes you happy will work. There aren't a lot of silly rules because Python projects can be simple.

• /scripts or /bin for that kind of command-line interface stuff
• /tests for your tests
• /lib for your C-language libraries
• /doc for most documentation
• /apidoc for the Epydoc-generated API docs.

And the top-level directory can contain README's, Config's and whatnot.

The hard choice is whether or not to use a /src tree. Python doesn't have a distinction between /src, /lib, and /bin like Java or C has.

Since a top-level /src directory is seen by some as meaningless, your top-level directory can be the top-level architecture of your application.

• /foo
• /bar
• /baz

I recommend putting all of this under the "name-of-my-product" directory. So, if you're writing an application named quux, the directory that contains all this stuff is named /quux.

Another project's PYTHONPATH, then, can include /path/to/quux/foo to reuse the QUUX.foo module.

In my case, since I use Komodo Edit, my IDE cuft is a single .KPF file. I actually put that in the top-level /quux directory, and omit adding it to SVN.

Answer 3

This blog post by Jean-Paul Calderone is commonly given as an answer in #python on Freenode.

Filesystem structure of a Python project

Do:

• name the directory something related to your project. For example, if your project is named "Twisted", name the top-level directory for its source files Twisted. When you do releases, you should include a version number suffix: Twisted-2.5.
• create a directory Twisted/bin and put your executables there, if you have any. Don't give them a .py extension, even if they are Python source files. Don't put any code in them except an import of and call to a main function defined somewhere else in your projects. (Slight wrinkle: since on Windows, the interpreter is selected by the file extension, your Windows users actually do want the .py extension. So, when you package for Windows, you may want to add it. Unfortunately there's no easy distutils trick that I know of to automate this process. Considering that on POSIX the .py extension is a only a wart, whereas on Windows the lack is an actual bug, if your userbase includes Windows users, you may want to opt to just have the .py extension everywhere.)
• If your project is expressable as a single Python source file, then put it into the directory and name it something related to your project. For example, Twisted/twisted.py. If you need multiple source files, create a package instead (Twisted/twisted/, with an empty Twisted/twisted/__init__.py) and place your source files in it. For example, Twisted/twisted/internet.py.
• put your unit tests in a sub-package of your package (note - this means that the single Python source file option above was a trick - you always need at least one other file for your unit tests). For example, Twisted/twisted/test/. Of course, make it a package with Twisted/twisted/test/__init__.py. Place tests in files like Twisted/twisted/test/test_internet.py.
• add Twisted/README and Twisted/setup.py to explain and install your software, respectively, if you're feeling nice.

Don't:

• put your source in a directory called src or lib. This makes it hard to run without installing.
• put your tests outside of your Python package. This makes it hard to run the tests against an installed version.
• create a package that only has a __init__.py and then put all your code into __init__.py. Just make a module instead of a package, it's simpler.
• try to come up with magical hacks to make Python able to import your module or package without having the user add the directory containing it to their import path (either via PYTHONPATH or some other mechanism). You will not correctly handle all cases and users will get angry at you when your software doesn't work in their environment.

Answer 4

According to Jean-Paul Calderone's Filesystem structure of a Python project:

Project/
|-- bin/
|   |-- project
|
|-- project/
|   |-- test/
|   |   |-- __init__.py
|   |   |-- test_main.py
|   |   
|   |-- __init__.py
|   |-- main.py
|
|-- setup.py
|-- README

Answer 5

Try starting the project using the python_boilerplate template. It largely follows the best practices (e.g. those here), but is better suited in case you find yourself willing to split your project into more than one egg at some point (and believe me, with anything but the simplest projects, you will. One common situation is where you have to use a locally-modified version of someone else's library).

• Where do you put the source?

  • For decently large projects it makes sense to split the source into several eggs. Each egg would go as a separate setuptools-layout under PROJECT_ROOT/src/<egg_name>.

• Where do you put application startup scripts?

  • The ideal option is to have application startup script registered as an entry_point in one of the eggs.

• Where do you put the IDE project cruft?

  • Depends on the IDE. Many of them keep their stuff in PROJECT_ROOT/.<something> in the root of the project, and this is fine.

• Where do you put the unit/acceptance tests?

  • Each egg has a separate set of tests, kept in its PROJECT_ROOT/src/<egg_name>/tests directory. I personally prefer to use py.test to run them.

• Where do you put non-Python data such as config files?

  • It depends. There can be different types of non-Python data.
    • "Resources", i.e. data that must be packaged within an egg. This data goes into the corresponding egg directory, somewhere within package namespace. It can be used via pkg_resources package.
    • "Config-files", i.e. non-Python files that are to be regarded as external to the project source files, but have to be initialized with some values when application starts running. During development I prefer to keep such files in PROJECT_ROOT/config. For deployment there can be various options. On Windows one can use %APP_DATA%/<app-name>/config, on Linux, /etc/<app-name> or /opt/<app-name>/config.
    • Generated files, i.e. files that may be created or modified by the application during execution. I would prefer to keep them in PROJECT_ROOT/var during development, and under /var during Linux deployment.
• Where do you put non-Python sources such as C++ for pyd/so binary extension modules?
  • Into PROJECT_ROOT/src/<egg_name>/native

Documentation would typically go into PROJECT_ROOT/doc or PROJECT_ROOT/src/<egg_name>/doc (this depends on whether you regard some of the eggs to be a separate large projects). Some additional configuration will be in files like PROJECT_ROOT/buildout.cfg and PROJECT_ROOT/setup.cfg.

Answer 6

Non-python data is best bundled inside your Python modules using the package_data support in setuptools. One thing I strongly recommend is using namespace packages to create shared namespaces which multiple projects can use -- much like the Java convention of putting packages in com.yourcompany.yourproject (and being able to have a shared com.yourcompany.utils namespace).

Re branching and merging, if you use a good enough source control system it will handle merges even through renames; Bazaar is particularly good at this.

Contrary to some other answers here, I'm +1 on having a src directory top-level (with doc and test directories alongside). Specific conventions for documentation directory trees will vary depending on what you're using; Sphinx, for instance, has its own conventions which its quickstart tool supports.

Please, please leverage setuptools and pkg_resources; this makes it much easier for other projects to rely on specific versions of your code (and for multiple versions to be simultaneously installed with different non-code files, if you're using package_data).