Exercise 46: A Project Skeleton
This will be where you start learning how to set up a good project "skeleton" directory. This skeleton directory will have all the basics you need to get a new project up and running. It will have your project layout, automated tests, modules, and install scripts. When you go to make a new project, just copy this directory to a new name and edit the files to get started.
Installing Python Packages
Before you can begin this exercise you need to install some software for Python by using a tool called "pip" to install new modules. Here's the problem though. You are at a point where it's difficult for me to help you do that and keep this book sane and clean. There are so many ways to install software on so many computers that I'd have to spend 10 pages walking you through every step, and let me tell you I am a lazy guy.
Rather than tell you how to do it exactly, I'm going to tell you what you should install, and then you tell you to watch the video that accompanies this exercise and follow along. You will have to struggle with this part of the exercise though as giving accurate and current installation instructions is tricky. Computers change frequently so you may have to do some research if you get stuck.
Install the following Python packages:
- pip from http://pypi.python.org/pypi/pip
- distribute from http://pypi.python.org/pypi/distribute
- nose from http://pypi.python.org/pypi/nose/
- virtualenv from http://pypi.python.org/pypi/virtualenv
Do not just download these packages and install them by hand. Instead see how other people recommend you install these packages and use them for your particular system. The process will be different for most versions of Linux, OSX, and definitely different for Windows.
I am warning you; this will be frustrating. In the business we call this "yak shaving." Yak shaving is any activity that is mind numblingly, irritatingly boring and tedious that you have to do before you can do something else that's more fun. You want to create cool Python projects, but you can't do that until you set up a skeleton directory, but you can't set up a skeleton directory until you install some packages, but you can't install packages until you install package installers, and you can't install package installers until you figure out how your system installs software in general, and so on.
Struggle through this anyway. Consider it your trial by annoyance to get into the programmer club. Every programmer has to do these annoying tedious tasks before they can do something cool.
Sometimes the Python installer does not add the C:\Python27\Script to the system PATH. If this is the case for you, go back and add this to the path just like you did for C:\Python27 in Exercise 0 with:
[Environment]::SetEnvironmentVariable("Path", "$env:Path;C:\Python27\Scripts", "User")
Creating the Skeleton Project Directory
First, create the structure of your skeleton directory with these commands:
$ mkdir projects $ cd projects/ $ mkdir skeleton $ cd skeleton $ mkdir bin NAME tests docs
I use a directory named projects to store all the various things I'm working on. Inside that directory I have my skeleton directory that I put the basis of my projects into. The directory NAME will be renamed to whatever you are calling your project's main module when you use the skeleton.
Next we need to set up some initial files. Here's how you do that on Linux/OSX:
$ touch NAME/__init__.py $ touch tests/__init__.py
Here's the same thing on Windows PowerShell:
$ new-item -type file NAME/__init__.py $ new-item -type file tests/__init__.py
That creates an empty Python module directories we can put our code in. Then we need to create a setup.py file we can use to install our project later if we want:
Edit this file so that it has your contact information and is ready to go for when you copy it.
Finally you will want a simple skeleton file for tests named tests/NAME_tests.py:
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Final Directory Structure
When you are done setting all of this up, your directory should look like mine here:
skeleton/ NAME/ __init__.py bin/ docs/ setup.py tests/ NAME_tests.py __init__.py
And from now on, you should run your commands from that work with this directory from this point. If you can't do ls -R and see this same structure, then you are in the wrong place. For example, people commonly go into the tests/ directory to try to run files there, which won't work. To run your application's tests, you would need to be above tests/ and this location I have above. So, if you try this:
$ cd tests/ # WRONG! WRONG! WRONG! $ nosetests ---------------------------------------------------------------------- Ran 0 tests in 0.000s OK
Then that is wrong! You have to be above tests, so assuming you made this mistake, you would fix it by doing this:
$ cd .. # get out of tests/ $ ls # CORRECT! you are now in the right spot NAME bin docs setup.py tests $ nosetests . ---------------------------------------------------------------------- Ran 1 test in 0.004s OK
Remember this because people make this mistake quite frequently.
Testing Your Setup
After you get all that installed you should be able to do this:
$ nosetests . ---------------------------------------------------------------------- Ran 1 test in 0.007s OK
I'll explain what this nosetests thing is doing in the next exercise, but for now if you do not see that, you probably got something wrong. Make sure you put __init__.py files in your NAME and tests directories and make sure you got tests/NAME_tests.py right.
Using the Skeleton
You are now done with most of your yak shaving. Whenever you want to start a new project, just do this:
- Make a copy of your skeleton directory. Name it after your new project.
- Rename (move) the NAME directory to be the name of your project or whatever you want to call your root module.
- Edit your setup.py to have all the information for your project.
- Rename tests/NAME_tests.py to also have your module name.
- Double check it's all working by using nosetests again.
- Start coding.
This exercise doesn't have Study Drills but a quiz you should complete:
- Read about how to use all of the things you installed.
- Read about the setup.py file and all it has to offer. Warning: it is not a very well-written piece of software, so it will be very strange to use.
- Make a project and start putting code into the module, then get the module working.
- Put a script in the bin directory that you can run. Read about how you can make a Python script that's runnable for your system.
- Mention the bin script you created in your setup.py so that it gets installed.
- Use your setup.py to install your own module and make sure it works, then use pip to uninstall it.
Common Student Questions
- Do these instructions work on Windows?
- They should, but depending on the version of Windows you may need to struggle with the setup a bit to get it working. Just keep researching and trying it until you get it, or see if you can ask a more experienced Python+Windows friend to help out.
- It seems I can't run nosetests on Windows?
- Sometimes the Python installer does not add the C:\Python27\Script to the system PATH. If this is the case for you, go back and add this to the path just like you did for C:\Python27 in Exercise 0.
- What do I put in the config dictionary in my setup.py?
- Make sure you read the documentation for distutils at http://docs.python.org/distutils/setupscript.html.
- I can't seem to load the NAME module and just get an ImportError.
- Make sure you made the NAME/__init__.py file. If you're on Windows make sure you didn't accidentally name it NAME/__init__.py.txt which happens by default with some editors.
- Why do we need a bin/ folder at all?
- This is just a standard place to put scripts that are run on the command line, not a place to put modules.
- Do you have a real world example project?
- There are many projects written in Python that do this, but try this simple one I created: https://gitorious.org/python-modargs.
- My nosetests run only shows one test being run. Is that right?
- Yes, that's what my output shows too.