Import Hook

maturin_import_hook is a package that provides a python import hook to automatically rebuild maturin projects when they are imported.

This reduces friction when developing mixed python/rust codebases because changes made to rust components take effect automatically like changes to python components do.

For import statements to trigger rebuilds, the hook must to be active (by calling install() or installing site-wide) and the maturin project being imported must be installed in editable mode (eg with maturin develop or pip install -e). Rebuilds are only triggered if the source code has changed, so the overhead is small if everything is up-to-date.

The hook also adds support for importing stand-alone .rs files by creating and building temporary maturin projects for them.


Run the following commands to install the package and optionally configure the hook to activate automatically when starting the interpreter.

pip install maturin_import_hook
python -m maturin_import_hook site install

In order to use site install, you must have write access to site-packages. It is recommended to use a virtual environment instead of installing into the system interpreter.

Alternatively, instead of using site install, put calls to maturin_import_hook.install() into any script where you want to use the import hook.


If the hook is installed site-wide, no code changes are required! just import a maturin project like normal and it will rebuild when necessary.

If the hook is not installed site-wide, call install() like so:

# install the import hook with default settings.
# can be skipped if installed site-wide (see above).
# must be called before importing any maturin project.
import maturin_import_hook

# when a maturin package that is installed in editable mode is imported,
# that package will be automatically recompiled if necessary.
import my_rust_package

# when a .rs file is imported a project will be created for it in the
# maturin build cache and the resulting library will be loaded.
# assuming subpackage/ defines a pyo3 module:
import subpackage.my_rust_script

The maturin project importer and the rust file importer can be used separately

from maturin_import_hook import rust_file_importer

from maturin_import_hook import project_importer

The import hook can be configured to control its behaviour

import maturin_import_hook
from maturin_import_hook.settings import MaturinSettings

        # ...
    # ...

The import hook is intended for use in development environments and not for production environments, so any calls to install() should ideally be removed before reaching production. This is another reason why installing site-wide is convenient.


The import hook is fairly robust and supports the following:

  • Supports all the binding types and project layouts supported by maturin.
  • Supports importing multiple maturin projects in the same script.
  • Supports importing stand-alone .rs files that use PyO3 bindings.
  • Supports importlib.reload() (currently not supported on Windows).
  • Detects source code changes of local path dependencies, not just the top-level project.
  • Can be used by multiple environments at once including with different interpreter versions. Each environment has a separate build cache.
  • Handles multiple scripts attempting to import/build packages simultaneously. Each build cache is protected with an exclusive lock. (One case where this is useful is tests using pytest-xdist).
  • Extensible (see Advanced Usage below)


The package provides a CLI interface for getting information such as the location and size of the build cache and managing the installation into For details, run:

python -m maturin_import_hook --help
  • site (info | install | uninstall)
    • Manage import hook installation in of the active environment.
  • cache (info | clear)
    • Manage the build cache of the active environment.
  • version
    • Show version info of the import hook and associated tools. Useful for providing information to bug reports.

Environment Variables

The import hook can be disabled by setting MATURIN_IMPORT_HOOK_ENABLED=0. This can be used to disable the import hook in production if you want to leave calls to install() in place.

Build files will be stored in an appropriate place for the current system but can be overridden by setting MATURIN_BUILD_DIR. These files can be deleted without causing any issues (unless a build is in progress). The precedence for storing build files is:

    • (Each environment will store its cache in a subdirectory of the given path).
  • <virtualenv_dir>/maturin_build_cache
  • <system_cache_dir>/maturin_build_cache
    • e.g. ~/.cache/maturin_build_cache on POSIX.

See the location being used with the CLI: python -m maturin_import_hook cache info


By default, the maturin_import_hook logger does not propagate to the root logger. This is so that INFO level messages are shown without having to configure logging (INFO level is normally not visible). The import hook also has extensive DEBUG level logging that generally would be more noise than useful. So by not propagating, DEBUG messages from the import hook are not shown even if the root logger has DEBUG level visible.

If you prefer, maturin_import_hook.reset_logger() can be called to undo the default configuration and propagate the messages as normal.

When debugging issues with the import hook, you should first call reset_logger() then configure the root logger to show DEBUG messages. You can also run with the environment variable RUST_LOG=maturin=debug to get more information from maturin.

import logging
logging.basicConfig(format='%(name)s [%(levelname)s] %(message)s', level=logging.DEBUG)
import maturin_import_hook

Advanced Usage

The import hook classes can be subclassed to further customize to specific use cases. For example settings can be configured per-project or loaded from configuration files.

import sys
from pathlib import Path
from maturin_import_hook.settings import MaturinSettings
from maturin_import_hook.project_importer import MaturinProjectImporter

class CustomImporter(MaturinProjectImporter):
    def get_settings(self, module_path: str, source_path: Path) -> MaturinSettings:
        return MaturinSettings(
            # ...

sys.meta_path.insert(0, CustomImporter())