frontend-editables

frontend-editables is a library for installing Python packages for development, originally created as a proof of concept for PEP 662. It supports installing prospective "editable" wheels using one of four different methods:

• "Lax" symlinking

  Symlinks top-level packages and modules only – the contents of packages can differ from those in the published distribution.

• "Strict" symlinking

  Symlinks files only, faithfully mirroring the structure of packages as they would appear in the published distribution.

• Redirector

  Generates a custom module finder which is used to load packages and modules from another location on disk and is injected in the sys.meta_path on start-up using a dynamic .pth file. This works similarly to the "lax" symlinking method – for more details, see editables.

• Static .pth file

  Creates a .pth file which lists directories containing the distribution's packages and modules, to add to the Python path. This will expose miscellaneous packages and modules which might be in the same folder.

Installation

$ python -m pip install frontend-editables

Basic usage

import sysconfig

import frontend_editables

path_mapping = ...  # Will have been returned by the backend.
installed_files = frontend_editables.install(
    [frontend_editables.PthFileInstaller],
    "name",
    sysconfig.get_path("purelib"),
    path_mapping,
)
# Then append the ``installed_files`` to the distribution's ``RECORD``,
# optionally by passing ``append_to_record=<path to RECORD>`` to ``install``.

The paths must map would-be wheel files to their absolute paths on disk; folder paths are invalid.

CLI

frontend_editables includes an extremely hacky CLI which serves a stopgap until editable installation is standardised. You can use this in place of python -m pip install -e .... The CLI supports all of the same layouts and installation methods supported by the library. Some examples:

• To install a project with a single module foo.py, symlinking it: python -m frontend_editables.transitional_cli -m strict_symlink foo.py foo.py.
• To install a project with a package foo, located in <project-root>/src/foo, with the aid of a pth file: python -m frontend_editables.transitional_cli -m pth_file src/foo foo.
• To install a project with multiple packages at different locations, using the redirecting path finder: python -m frontend_editables.transitional_cli -m redirector {src/,}foo {lib/,}bar

Editable distributions can be uninstalled with pip as normal.

usage: python -m frontend_editables.transitional_cli [-h] --method
                                                     {lax_symlink,pth_file,redirector,strict_symlink}
                                                     [--spec SPEC]
                                                     path_pairs [path_pairs ...]

Wacky transitional editable project installer.

positional arguments:
  path_pairs            pairs of path on disk and corresponding path in the
                        virtual wheel (posix)

optional arguments:
  -h, --help            show this help message and exit
  --method {lax_symlink,pth_file,redirector,strict_symlink}, -m {lax_symlink,pth_file,redirector,strict_symlink}
                        editable installation method to use (default: None)
  --spec SPEC           requirement specifier (default: .)

Contributing

You can use frontend-editables to install frontend-editables for development:

$ PYTHONPATH=src python -m frontend_editables.transitional_cli \
    --spec .[test] {src/,}frontend_editables

Before opening a merge request, install nox and run nox. The type checking step has an external dependency on npm.

Happy hacking!