feat: add extras mechanism to finer-grained dependency selection

Inspired by: #36 (comment).

This commit includes the extra-dependencies mechanism of setuptools to overcome limitations specific to certain dependencies
(e.g. no support for some Python interpreter versions).

The changes use the following conventions for extras names:

- `[all]`: install all dependencies from all extras
- `[X-sampler]`: install all dependencies to make X sampler to work
- `[X-loss]`: install all dependencies to make X loss function to work.

We do not have yet an example for the last item for the moment; but for "forward-compatibility" of the nomenclature, we leave the -sampler suffix.

E.g. for GPy, we could have the extra called gp-sampler, that installs GPy on-demand, and not installed if not needed by the user.

This commit also includes a mechanism to handle import errors for the non-installed dependencies for some component.
Such mechanism provides a useful message to the user, e.g. it raises an exception with a useful error message
pointing out to the missing extra in its local installation of black-it.

README.md

@@ -38,19 +38,34 @@ matter of days, with no need to reimplement all the plumbings from scratch.
 
 This project requires Python v3.8 or later.
 
-To install the latest version of the package from [PyPI](https://pypi.org/project/black-it/):
+To install the latest version of the package from [PyPI](https://pypi.org/project/black-it/), with all the extra dependencies (recommended):
 ```
-pip install black-it
+pip install "black-it[all]"
 ```
 
 Or, directly from GitHub:
 
 ```
-pip install git+https://github.com/bancaditalia/black-it.git#egg=black-it
+pip install git+https://github.com/bancaditalia/black-it.git#egg="black-it[all]"
 ```
 
 If you'd like to contribute to the package, please read the [CONTRIBUTING.md](./CONTRIBUTING.md) guide.
 
+### Feature-specific Package Dependencies
+
+We use the [optional dependencies mechanism of `setuptools`](https://setuptools.pypa.io/en/latest/userguide/dependency_management.html#optional-dependencies) 
+(also called _extras_) to allow users to avoid dependencies for features they don't use.
+
+For the basic features of the package, you can install the `black-it` package without extras, e.g. `pip install black-it`.
+However, for certain components, you will need to install some more extras using the syntax `pip install black-it[extra-1,extra-2,...]`.
+
+For example, the [Gaussian Process Sampler](https://bancaditalia.github.io/black-it/samplers/#black_it.samplers.gaussian_process.GaussianProcessSampler)
+depends on the Python package [`GPy`](https://github.com/SheffieldML/GPy/).
+If the Gaussian Process sampler is not needed by your application, you can avoid its installation by just installing `black-it` as explained above. 
+However, if you need the sampler, you must install `black-it` with the `gp-sampler` extra: `pip install black-it[gp-sampler]`. 
+
+The special extra `all` will install all the dependencies.
+
 ## Quick Example
 
 The GitHub repo of Black-it contains a series ready-to-run calibration examples.

black_it/_load_dependency.py

@@ -0,0 +1,112 @@
+# Black-box ABM Calibration Kit (Black-it)
+# Copyright (C) 2021-2023 Banca d'Italia
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+"""
+Python module to handle extras dependencies loading and import errors.
+
+This is a private module of the library. There should be no point in using it directly from client code.
+"""
+
+import sys
+from typing import Optional
+
+# known extras and their dependencies
+_GPY_PACKAGE_NAME = "GPy"
+_GP_SAMPLER_EXTRA_NAME = "gp-sampler"
+
+_XGBOOST_PACKAGE_NAME = "xgboost"
+_XGBOOST_SAMPLER_EXTRA_NAME = "xgboost-sampler"
+
+
+class DependencyNotInstalled(Exception):
+    """Library exception for when a required dependency is not installed."""
+
+    def __init__(self, component_name: str, package_name: str, extra_name: str) -> None:
+        """Initialize the exception object."""
+        message = (
+            f"Cannot import package '{package_name}', required by component {component_name}. "
+            f"To solve the issue, you can install the extra '{extra_name}': pip install black-it[{extra_name}]"
+        )
+        super().__init__(message)
+
+
+class GPyNotSupportedOnPy311Exception(Exception):
+    """Specific exception class for import error of GPy on Python 3.11."""
+
+    __ERROR_MSG = (
+        f"The GaussianProcessSampler depends on '{_GPY_PACKAGE_NAME}', which is not supported on Python 3.11; "
+        f"see https://github.com/bancaditalia/black-it/issues/36"
+    )
+
+    def __init__(self) -> None:
+        """Initialize the exception object."""
+        super().__init__(self.__ERROR_MSG)
+
+
+def _check_import_error_else_raise_exception(
+    import_error: Optional[ImportError],
+    component_name: str,
+    package_name: str,
+    black_it_extra_name: str,
+) -> None:
+    """
+    Check an import error; raise the DependencyNotInstalled exception with a useful message.
+
+    Args:
+        import_error: the ImportError object generated by the failed attempt. If None, then no error occurred.
+        component_name: the component for which the dependency is needed
+        package_name: the Python package name of the dependency
+        black_it_extra_name: the name of the black-it extra to install to solve the issue.
+    """
+    if import_error is None:
+        # nothing to do.
+        return
+
+    # an import error happened; we need to raise error to the caller
+    raise DependencyNotInstalled(component_name, package_name, black_it_extra_name)
+
+
+def _check_gpy_import_error_else_raise_exception(
+    import_error: Optional[ImportError],
+    component_name: str,
+    package_name: str,
+    black_it_extra_name: str,
+) -> None:
+    """
+    Check GPy import error and if an error occurred, raise erorr with a useful error message.
+
+    We need to handle two cases:
+
+    - the user is using Python 3.11: the GPy package cannot be installed there;
+        see https://github.com/SheffieldML/GPy/issues/998
+    - the user did not install the 'gp-sampler' extra.
+
+    Args:
+        import_error: the ImportError object generated by the failed attempt. If None, then no error occurred.
+        component_name: the component for which the dependency is needed
+        package_name: the Python package name of the dependency
+        black_it_extra_name: the name of the black-it extra to install to solve the issue.
+    """
+    if import_error is None:
+        # nothing to do.
+        return
+
+    if sys.version_info == (3, 11):
+        raise GPyNotSupportedOnPy311Exception()
+
+    _check_import_error_else_raise_exception(
+        import_error, component_name, package_name, black_it_extra_name
+    )

black_it/samplers/gaussian_process.py

@@ -20,14 +20,26 @@
 from enum import Enum
 from typing import Optional, Tuple, cast
 
-import GPy
 import numpy as np
-from GPy.models import GPRegression
 from numpy.typing import NDArray
 from scipy.special import erfc  # pylint: disable=no-name-in-module
 
+from black_it._load_dependency import (
+    _GP_SAMPLER_EXTRA_NAME,
+    _GPY_PACKAGE_NAME,
+    _check_import_error_else_raise_exception,
+)
 from black_it.samplers.surrogate import MLSurrogateSampler
 
+_GPY_IMPORT_ERROR: Optional[ImportError]
+try:
+    import GPy
+    from GPy.models import GPRegression
+except ImportError as e:
+    _GPY_IMPORT_ERROR = e
+else:
+    _GPY_IMPORT_ERROR = None
+
 
 class _AcquisitionTypes(Enum):
     """Enumeration of allowed acquisition types."""
@@ -71,6 +83,8 @@ def __init__(  # pylint: disable=too-many-arguments
             optimize_restarts: number of independent random trials of the optimization of the GP hyperparameters
             acquisition: type of acquisition function, it can be 'expected_improvement' of simply 'mean'
         """
+        self.__check_gpy_import_error()
+
         self._validate_acquisition(acquisition)
 
         super().__init__(
@@ -81,6 +95,13 @@ def __init__(  # pylint: disable=too-many-arguments
         self.acquisition = acquisition
         self._gpmodel: Optional[GPRegression] = None
 
+    @classmethod
+    def __check_gpy_import_error(cls) -> None:
+        """Check if an import error happened while attempting to import the 'GPy' package."""
+        _check_import_error_else_raise_exception(
+            _GPY_IMPORT_ERROR, cls.__name__, _GPY_PACKAGE_NAME, _GP_SAMPLER_EXTRA_NAME
+        )
+
     @staticmethod
     def _validate_acquisition(acquisition: str) -> None:
         """

black_it/samplers/xgboost.py

@@ -19,15 +19,27 @@
 from typing import Optional, cast
 
 import numpy as np
-import xgboost as xgb
 from numpy.typing import NDArray
 
+from black_it._load_dependency import (
+    _XGBOOST_PACKAGE_NAME,
+    _XGBOOST_SAMPLER_EXTRA_NAME,
+    _check_import_error_else_raise_exception,
+)
 from black_it.samplers.surrogate import MLSurrogateSampler
 
 MAX_FLOAT32 = np.finfo(np.float32).max
 MIN_FLOAT32 = np.finfo(np.float32).min
 EPS_FLOAT32 = np.finfo(np.float32).eps
 
+_XGBOOST_IMPORT_ERROR: Optional[ImportError]
+try:
+    import xgboost as xgb
+except ImportError as e:
+    _XGBOOST_IMPORT_ERROR = e
+else:
+    _XGBOOST_IMPORT_ERROR = None
+
 
 class XGBoostSampler(MLSurrogateSampler):
     """This class implements xgboost sampling."""
@@ -64,6 +76,7 @@ def __init__(  # pylint: disable=too-many-arguments
         References:
             Lamperti, Roventini, and Sani, "Agent-based model calibration using machine learning surrogates"
         """
+        self.__check_xgboost_import_error()
         super().__init__(
             batch_size, random_state, max_deduplication_passes, candidate_pool_size
         )
@@ -75,6 +88,16 @@ def __init__(  # pylint: disable=too-many-arguments
         self._n_estimators = n_estimators
         self._xg_regressor: Optional[xgb.XGBRegressor] = None
 
+    @classmethod
+    def __check_xgboost_import_error(cls) -> None:
+        """Check if an import error happened while attempting to import the 'xgboost' package."""
+        _check_import_error_else_raise_exception(
+            _XGBOOST_IMPORT_ERROR,
+            cls.__name__,
+            _XGBOOST_PACKAGE_NAME,
+            _XGBOOST_SAMPLER_EXTRA_NAME,
+        )
+
     @property
     def colsample_bytree(self) -> float:
         """Get the colsample_bytree parameter."""

pyproject.toml

@@ -34,7 +34,6 @@ classifiers = [
 
 [tool.poetry.dependencies]
 python = ">=3.8,<3.11"
-GPy = "^1.10.0"
 ipywidgets = "^7.7.0"
 matplotlib = "^3.5.2"
 numpy = ">=1.23.3,<1.24.0"
@@ -43,7 +42,6 @@ scikit-learn = "^1.1.0"
 seaborn = "^0.11.2"
 statsmodels = "^0.13.2"
 tables = "^3.7.0"
-xgboost = "^1.7.2"
 
 [tool.poetry.dev-dependencies]
 bandit = "^1.7.4"
@@ -84,6 +82,11 @@ tox = "^3.25.0"
 twine = "^4.0.0"
 vulture = "^2.3"
 
+[project.optional-dependencies]
+gp-sampler = ["GPy~=1.10.0"]
+xgboost-sampler = ["xgboost~=1.7.2"]
+all = ["GPy~=1.10.0", "xgboost~=1.7.2"]
+
 [build-system]
 requires = ["poetry-core>=1.0.0"]
 build-backend = "poetry.core.masonry.api"

tests/test_calibrator.py

@@ -38,8 +38,11 @@
 from black_it.search_space import SearchSpace
 
 from .fixtures.test_models import NormalMV  # type: ignore
+from .utils.base import no_gpy_installed, no_xgboost_installed
 
 
+@no_gpy_installed
+@no_xgboost_installed
 class TestCalibrate:  # pylint: disable=too-many-instance-attributes,attribute-defined-outside-init
     """Test the Calibrator.calibrate method."""
 

tests/test_samplers/test_gaussian_process.py

@@ -22,6 +22,9 @@
 
 from black_it.samplers.gaussian_process import GaussianProcessSampler, _AcquisitionTypes
 from black_it.search_space import SearchSpace
+from tests.utils.base import no_gpy_installed
+
+pytestmark = no_gpy_installed
 
 
 class TestGaussianProcess2D:  # pylint: disable=attribute-defined-outside-init

tests/test_samplers/test_xgboost.py

@@ -23,6 +23,10 @@
 from black_it.search_space import SearchSpace
 
 from ..fixtures.test_models import BH4  # type: ignore
+from ..utils.base import no_xgboost_installed
+
+pytestmark = no_xgboost_installed
+
 
 expected_params = np.array([[0.24, 0.26], [0.26, 0.02], [0.08, 0.24], [0.15, 0.15]])
 

tests/utils/base.py

@@ -16,14 +16,19 @@
 
 """Generic utility functions."""
 import dataclasses
+import importlib
 import shutil
 import signal
 import subprocess  # nosec B404
+import sys
+import types
 from functools import wraps
-from typing import Callable, List, Type, Union
+from typing import Any, Callable, List, Optional, Type, Union
 
 import pytest
+from _pytest.mark.structures import MarkDecorator
 
+from black_it._load_dependency import _GPY_PACKAGE_NAME, _XGBOOST_PACKAGE_NAME
 from tests.conftest import DEFAULT_SUBPROCESS_TIMEOUT
 
 
@@ -170,3 +175,30 @@ def wrapper(*args, **kwargs):  # type: ignore
         return wrapper
 
     return decorator
+
+
+def try_import_else_none(module_name: str) -> Optional[types.ModuleType]:
+    """Try to import a module; if it fails, return None."""
+    try:
+        return importlib.import_module(module_name)
+    except ImportError:
+        return None
+
+
+def try_import_else_skip(package_name: str, **skipif_kwargs: Any) -> MarkDecorator:
+    """Try to import the package; else skip the test(s)."""
+    return pytest.mark.skipif(
+        try_import_else_none(package_name) is None,
+        reason=f"Cannot run the test because the package '{package_name}' is not installed",
+        **skipif_kwargs,
+    )
+
+
+no_python311_for_gpy = pytest.mark.skipif(
+    (3, 11) <= sys.version_info < (3, 12),
+    reason="GPy not supported on Python 3.11, see: https://github.com/bancaditalia/black-it/issues/36",
+)
+
+
+no_gpy_installed = no_python311_for_gpy(try_import_else_skip(_GPY_PACKAGE_NAME))
+no_xgboost_installed = try_import_else_skip(_XGBOOST_PACKAGE_NAME)

tox.ini

@@ -19,6 +19,7 @@ deps =
     ; Other test dependencies
     ; ...
     mistletoe>=0.8.2,<0.9.0
+extras = all
 
 commands =
     pytest --basetemp={envtmpdir} --doctest-modules \