Packaging Python Classes as a Wheel
Let's get this wheel rolling.
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Recently, while working on a project where we were using Python, I realized how easy the Java package mechanism makes it, to organize and reuse common classes and functions.
Due to my Java hangover, I organized the common classes and functions in a directory hierarchy like
util package contained a few classes for UUID creation as well as classes for date and time manipulation. After placing the files in the above-mentioned directory, I started developing the application as a micro-service. I placed the micro-service code in the directory
com.<company>.<project>.<service>. While trying to use the date and time classes in the micro-service, I used the syntax
from com.<company>.<project>.util.mydatetime import MyDateTime.
This syntax threw a compilation error, as the Python environment was not able to find the
com/company/project/util directory. I was puzzled by this and after some time realized that the Python environment was expecting the
MyDateTime class in the
com/company/project/service/com/company/project/util directory. Compared to this, when the package path is mentioned in each Java class, the Java environment resolves the reference to the class.
After some exploration, I settled on packaging the common classes as a wfheel. Once a package is made into a wheel, it can be installed like any other Python package, using the pip command. Upon installation, the package is installed in the same place where external site packages are installed using
The advantage of a wheel is that after installation, we can refer to the class as
com.<company>.<project>.util from anywhere in the code and it will be resolved. The limitation is that each time the common code is updated, we have to repackage the wheel and distribute it to all users. Each user has to uninstall the existing wheel and then install the updated wheel.
As we were in the development phase, we had to frequently update the wheel and make it available to other members of the development team. To make the task of building and managing the wheel, I wrote a few Windows batch files. In the remaining part of the article, I am sharing the batch files. I also have a few helper batch files that make my task of file management a bit easier.
Note: Though the code snippet mentions PowerShell, the commands have to be executed on Windows Command Prompt by saving each one into a .bat file
Delete Backup Files - del-bak.bat
Delete Dist Directory - del-dist.bat
Before creating the actual wheel, I thought it better to delete the 'dist' directory that is referred by Python during wheel creation. This ensures that files that are no longer part of the project do not continue to be included in the wheel.
Delete Log Files - del-log.bat
Make Wheel - make-wheel.bat
Before building the wheel, delete the 'dist' directory, set the package name as environment variable, and then invoke a command to make the wheel.
Install the Wheel - wheel-install.bat
Uninstall the wheel - wheel-uninstall.bat
Run the Steps in Sequence - refresh.bat
I packaged the various steps related to wheels into a helper batch file. The file uninstalls the existing package and makes the new wheel. Once the wheel is created, it is installed.
Set Package Name - set-package-name.bat
Set the name of the package for use by other batch files.
While the batch files make the task of creating and installing the wheel easy, the key to making the wheel is the setup file.
By creating these helper files, each time I make changes to the code and test it, I simply run
refresh.bat and all the work is done one by one. I only need to keep pressing the 'Enter' key a couple of times - while it is not required, I use it to keep track of the steps.
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