reorder-editable 0.1.2

naive implementation to reorder my easy-install.pth file

reorder_editable

Naive implementation to reorder my easy-install.pth file

It is meant to be used to make sure editable namespace packages in my easy-install.pth are in a specific order.

Editable Namespace Packages?

To expand:

• Editable: A package that is installed in editable mode (like pip install -e), i.e., if you make any changes to the code, your changes are reflected immediately. Is useful for packages that you change very often, or while developing. See the site module docs for more information on how this modifies sys.path
• Namespace Packages: Namespace packages let you split a package across multiple directories on disk, merging any submodules into the parent package. For more info, see PEP420

Sidenote: A namespace package is typically installed using setuptools.find_namespace_packages, instead of setuptools.find_packages

So, an editable, namespace package is multiple directories on disk all installed as a single package. If any changes are made to any of the directories, the package updates immediately.

This is the current strategy HPI uses for extension. I can keep up to date with upstream and manage my own modules by installing both (or more) like:

pip install -e /local/clone/of/karlicoss/HPI
pip install -e /local/clone/of/seanbreckenridge/HPI

This creates a file in your python installation that looks like this:

$ cat ~/.local/lib/python3.9/site-packages/easy-install.pth
/home/sean/Repos/karlicoss/HPI
/home/sean/Repos/seanbreckenridge/HPI

... to link those installs to the paths you specified.

However, for namespace packages in particular, the order that those directories appear in the easy-install.pth matter. Since items in easy-install.pth are added to sys.path in order, that determines which order python searches for packages in when trying to resolve imports.

For example, given the following structure:

.
├── my_HPI
│   ├── package_name
│   │   ├── a.py
│   │   └── b.py
│   └── setup.py
└── upstream_HPI
    ├── package_name
    │   ├── a.py
    │   └── c.py
    └── setup.py

If easy-install.pth was ordered:

my_HPI
upstream_HPI

import package_name.a would import my_HPI/package_name/a.py, instead of upstream_HPI/package_name/a.py, because that's the first item it matched in the easy-install.pth. This process is described much more technically in the PEP

This is pretty much a native plugin system, as it lets me overlay specific files/modules with personal changes in my directory structure, while keeping up to date with the upstream changes. There's very little overhead since all I'm doing is adding python files to a local directory and the globally installed package immediately updates.

In the example above, I can still import package_name.b and package_name.c as normal, even though they're in different directory structures.

---

Now - to the problem this aims to solve.

There is no way to manage your easy-install.pth file, to make sure packages are in a defined order.

In particular, I want my repository to be above my fork of the upstream repo, as that means I'm able to override files from upstream with my own changes, while maintaining two separate directories - which prevents me from running into merge conflicts. While developing, I may end up uninstalling/reinstalling one or more of my local clones of the HPI packages, and that leads to it resolving to a file from the upstream repository, when I was expecting my own -- leading to confusing and difficult to debug errors.

The script itself is pretty basic. All easy-install.pth is lines of absolute paths pointing to directories, so this just takes the directories you pass as positional arguments and makes sure they're in that order in your easy-install.pth file by shuffling it around.

I don't believe this breaks and built-in python/pip behaviour, but please open a PR/Issue if you think there's an issue/this could be improved.

Should be noted that if you've already imported a namespace module the __path__ is cached (which determines the import order), so this (probably?) won't work if you re-order the easy-install.pth file after the module has already been loaded -- at least not for that python process/unless you re-import it by messing with sys.modules and re-import the library.

Still - at least this tells me when it breaks, and fixes it for the next time python runs, so I don't have to worry about it/do it manually.

The actual hack that runs in my HPI configuration script, so I never have to think about this again:

def repo(name: str) -> str:
    return path.join(environ["REPOS"], name)


# https://github.com/seanbreckenridge/reorder_editable
# if my easy-install.pth file was ordered wrong, fix it and exit!
from reorder_editable import Editable

if Editable().reorder([repo("HPI"), repo("HPI-fork")]):
    # this is true if we actually reordered the path, else path was already ordered
    print(
        "easy-install.pth was ordered wrong! It has been reordered, exiting to apply changes...",
        file=sys.stderr,
    )
    sys.exit(0)

Note: Either install all editable packages as --user, or all at the system level. Otherwise, the lines of text/packages are split across two separate easy-install.pth files, and its not possible to reorder.

Installation

Requires python3.7+

To install with pip, run:

python3 -m pip install reorder_editable

Can always be accessed like python3 -m reorder_editable, if your python local bin directory isn't on your $PATH

Usage

Usage: reorder_editable [OPTIONS] COMMAND [ARGS]...

  Manage your editable packages - your easy-install.pth file

Options:
  --help  Show this message and exit.

Commands:
  cat      print easy-install.pth contents
  check    check easy-install.pth
  locate   print easy-install.pth file location
  reorder  reorder easy-install.pth

To reorder:

Usage: reorder_editable reorder [OPTIONS] DIRECTORY...

  If the order specified in your easy-install.pth doesn't match the order of
  the directories specified as positional arguments, reorder them so that it
  does. This always places items you're reordering at the end of your easy-
  install.pth so make sure to include all items you care about the order of

  Also fails if one of the paths you provide doesn't exist, or it isn't
  already in you easy-install.pth

  e.g.
  reorder_editable reorder ./path/to/repo /another/path/to/repo

  If ./path/to/repo was below /another/path/to/repo, this would reorder
  items in your config file to fix it so that ./path/to/repo is above
  /another/path/to/repo

Options:
  -e, --easy-install-location TEXT
                                  Manually provide path to easy-install.pth
  --help                          Show this message and exit.

As an example using the descriptions above, If I wanted to make sure my_HPI was above upstream_HPI, I'd run:

$ python3 -m reorder_editable reorder ./my_HPI ./upstream_HPI

Tests

git clone 'https://github.com/seanbreckenridge/reorder_editable'
cd ./reorder_editable
pip install '.[testing]'
mypy ./reorder_editable
pytest