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Design principles

or Why I'm Refusing to Add a Feature

There are some principles in the design of Pynsist which have led me to turn down potentially useful options. I've tried to explain them here so that I can link to this rather than summarising them each time.

  1. Pynsist is largely a simplifying wrapper around NSIS: it provides an easy way to do a subset of the things NSIS can do. All simplifying wrappers come under pressure from people who want to do something just outside what the wrapper currently covers: they'd love to use the wrapper, if it just had one more option. But if we keep adding options, eventually the simplifying wrapper becomes a convoluted layer of extra complexity over the original system.
  2. I'm very keen to keep installers as simple as possible. There are all sorts of clever things we could do at install time. But it's much harder to write and test the NSIS install code than the Python build code, and errors when the end user installs your software are a bigger problem than errors when you build it, because you're better able to understand and fix them. So Pynsist does as much as possible at build time so that the installer can be simple.
  3. Pynsist has a limited scope: it builds Windows installers for Python applications. Mostly GUI applications, but it does also have support for adding command-line tools. I don't plan to add support for other target platforms or languages.

If you need more flexibility

If you want to do something which Pynsist doesn't support, there are several ways it can still help you:

  • Generate an nsi script: You can run Pynsist once with the --no-makensis option. In the build directory, you'll find a file installer.nsi, which is the script for your installer. You can modify this and run makensis installer.nsi yourself to build the installer.
  • Write a custom template: Pynsist uses Jinja templates to create the nsi script. You can write a custom template and specify it in the :ref:`build_config` in your config file. Custom templates can inherit from the templates in Pynsist and override blocks, so you have a lot of control over the installer this way.
  • Cannibalise the code: Pull out whatever pieces are useful to you from Pynsist and use them in your build scripts. There are the installer templates, code to find and download wheels from PyPI, to download Python itself, to create command-line entry points, to find makensis.exe on Windows, and so on. You can take specific bits to reuse, or copy the whole thing and apply some changes.