"""The classloader provides utilities to dynamically load classes and modules."""
import inspect
from importlib import resources
import sys
from importlib import import_module
from importlib.util import find_spec, resolve_name
from types import ModuleType
from typing import Optional, Sequence, Type
from ..core.error import BaseError
[docs]class ModuleLoadError(BaseError):
"""Module load error."""
[docs]class ClassNotFoundError(BaseError):
"""Class not found error."""
[docs]class ClassLoader:
"""Class used to load classes from modules dynamically."""
[docs] @classmethod
def load_module(cls, mod_path: str, package: str = None) -> ModuleType:
"""Load a module by its absolute path.
Args:
mod_path: the absolute or relative module path
package: the parent package to search for the module
Returns:
The resolved module or `None` if the module cannot be found
Raises:
ModuleLoadError: If there was an error loading the module
"""
if package:
# preload parent package
if not cls.load_module(package):
return None
# must treat as a relative import
if not mod_path.startswith("."):
mod_path = f".{mod_path}"
full_path = resolve_name(mod_path, package)
if full_path in sys.modules:
return sys.modules[full_path]
if "." in mod_path:
parent_mod_path, mod_name = mod_path.rsplit(".", 1)
if parent_mod_path and parent_mod_path[-1] != ".":
parent_mod = cls.load_module(parent_mod_path, package)
if not parent_mod:
return None
package = parent_mod.__name__
mod_path = f".{mod_name}"
# Load the module spec first
# this means that a later ModuleNotFoundError indicates a code issue
spec = find_spec(mod_path, package)
if not spec:
return None
try:
return import_module(mod_path, package)
except ModuleNotFoundError as e:
raise ModuleLoadError(
f"Unable to import module {full_path}: {str(e)}"
) from e
[docs] @classmethod
def load_class(
cls,
class_name: str,
default_module: Optional[str] = None,
package: Optional[str] = None,
):
"""Resolve a complete class path (ie. typing.Dict) to the class itself.
Args:
class_name: the class name
default_module: the default module to load, if not part of in the class name
package: the parent package to search for the module
Returns:
The resolved class
Raises:
ClassNotFoundError: If the class could not be resolved at path
ModuleLoadError: If there was an error loading the module
"""
if "." in class_name:
# import module and find class
mod_path, class_name = class_name.rsplit(".", 1)
elif default_module:
mod_path = default_module
else:
raise ClassNotFoundError(
f"Cannot resolve class name with no default module: {class_name}"
)
mod = cls.load_module(mod_path, package)
if not mod:
raise ClassNotFoundError(f"Module '{mod_path}' not found")
resolved = getattr(mod, class_name, None)
if not resolved:
raise ClassNotFoundError(
f"Class '{class_name}' not defined in module: {mod_path}"
)
if not isinstance(resolved, type):
raise ClassNotFoundError(
f"Resolved value is not a class: {mod_path}.{class_name}"
)
return resolved
[docs] @classmethod
def load_subclass_of(cls, base_class: Type, mod_path: str, package: str = None):
"""Resolve an implementation of a base path within a module.
Args:
base_class: the base class being implemented
mod_path: the absolute module path
package: the parent package to search for the module
Returns:
The resolved class
Raises:
ClassNotFoundError: If the module or class implementation could not be found
ModuleLoadError: If there was an error loading the module
"""
mod = cls.load_module(mod_path, package)
if not mod:
raise ClassNotFoundError(f"Module '{mod_path}' not found")
# Find an the first declared class that inherits from
try:
imported_class = next(
obj
for name, obj in inspect.getmembers(mod, inspect.isclass)
if issubclass(obj, base_class) and obj is not base_class
)
except StopIteration:
raise ClassNotFoundError(
f"Could not resolve a class that inherits from {base_class}"
) from None
return imported_class
[docs] @classmethod
def scan_subpackages(cls, package: str) -> Sequence[str]:
"""Return a list of sub-packages defined under a named package."""
if "." in package:
package, sub_pkg = package.split(".", 1)
else:
sub_pkg = "."
try:
package_path = resources.files(package)
except FileNotFoundError:
raise ModuleLoadError(f"Undefined package {package}")
if not (package_path / sub_pkg).is_dir():
raise ModuleLoadError(f"Undefined package {package}")
found = []
joiner = "" if sub_pkg == "." else f"{sub_pkg}."
sub_path = package_path / sub_pkg
for item in sub_path.iterdir():
if (item / "__init__.py").exists():
found.append(f"{package}.{joiner}{item.name}")
return found
[docs]class DeferLoad:
"""Helper to defer loading of a class definition."""
def __init__(self, cls_path: str):
"""Initialize the `DeferLoad` instance with a qualified class path."""
self._cls_path = cls_path
self._inst = None
def __call__(self, *args, **kwargs):
"""Magic method to call the `DeferLoad` as a function."""
return (self.resolved)(*args, **kwargs)
@property
def resolved(self):
"""Accessor for the resolved class instance."""
if not self._inst:
self._inst = ClassLoader.load_class(self._cls_path)
return self._inst