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Python:importlib

Python importlib 라이브러리 사용방법 정리.

String import 

import av

대신 

import importlib
av = importlib.import_module('av')

이 가능하다.

Path import

For Python 3.5+ use: 

import importlib.util
spec = importlib.util.spec_from_file_location("module.name", "/path/to/file.py")
foo = importlib.util.module_from_spec(spec)
spec.loader.exec_module(foo)
foo.MyClass()

For Python 3.3 and 3.4 use: 

from importlib.machinery import SourceFileLoader

foo = SourceFileLoader("module.name", "/path/to/file.py").load_module()
foo.MyClass()

(Although this has been deprecated in Python 3.4.)

For Python 2 use: 

import imp

foo = imp.load_source('module.name', '/path/to/file.py')
foo.MyClass()

There are equivalent convenience functions for compiled Python files and DLLs.

See also http://bugs.python.org/issue21436

위의 내용은, exec 함수 사용시 모듈 로드 때문에 검색하게 되었다.

Loader

BuiltinImporter 

class BuiltinImporter:
    """Meta path import for built-in modules.

    All methods are either class or static methods to avoid the need to
    instantiate the class.

    """

    @classmethod
    def module_repr(cls, module):
        return "<module '{}' (built-in)>".format(module.__name__)

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find the built-in module.

        If 'path' is ever specified then the search is considered a failure.

        """
        if path is not None:
            return None
        return cls if _imp.is_builtin(fullname) else None

    @classmethod
    @set_package
    @set_loader
    @_requires_builtin
    def load_module(cls, fullname):
        """Load a built-in module."""
        is_reload = fullname in sys.modules
        try:
            return _call_with_frames_removed(_imp.init_builtin, fullname)
        except:
            if not is_reload and fullname in sys.modules:
                del sys.modules[fullname]
            raise

    @classmethod
    @_requires_builtin
    def get_code(cls, fullname):
        """Return None as built-in modules do not have code objects."""
        return None

    @classmethod
    @_requires_builtin
    def get_source(cls, fullname):
        """Return None as built-in modules do not have source code."""
        return None

    @classmethod
    @_requires_builtin
    def is_package(cls, fullname):
        """Return False as built-in modules are never packages."""
        return False

import_from_string 구현

unicorn 의 importer.py 파일에 구현되어 있다. 

import importlib
from typing import Any


class ImportFromStringError(Exception):
    pass


def import_from_string(import_str: Any) -> Any:
    if not isinstance(import_str, str):
        return import_str

    module_str, _, attrs_str = import_str.partition(":")
    if not module_str or not attrs_str:
        message = (
            'Import string "{import_str}" must be in format "<module>:<attribute>".'
        )
        raise ImportFromStringError(message.format(import_str=import_str))

    try:
        module = importlib.import_module(module_str)
    except ModuleNotFoundError as exc:
        if exc.name != module_str:
            raise exc from None
        message = 'Could not import module "{module_str}".'
        raise ImportFromStringError(message.format(module_str=module_str))

    instance = module
    try:
        for attr_str in attrs_str.split("."):
            instance = getattr(instance, attr_str)
    except AttributeError:
        message = 'Attribute "{attrs_str}" not found in module "{module_str}".'
        raise ImportFromStringError(
            message.format(attrs_str=attrs_str, module_str=module_str)
        )

    return instance

Approximation of importlib.import_module (find_spec)

공식 도큐멘테이션에서는 importlib.import_module() 의 간소화된 구현을 예시로써 제공하고 있다. 이 예시를 통해 임포트 함수의 구현 방식에 대해 파악할 수 있으며, importlib의 각종 API들이 어떤 식으로 작동하는 지를 보여주고 있어 사용자 정의 임포트 함수를 작성하는 데에 유용하게 쓰일 수 있다. 

# https://docs.python.org/ko/3/library/importlib.html 출처
import importlib.util
import sys

def import_module(name, package=None):
    """An approximate implementation of import."""
    absolute_name = importlib.util.resolve_name(name, package)
    try:
        return sys.modules[absolute_name]
    except KeyError:
        pass

    path = None
    if '.' in absolute_name:
        parent_name, _, child_name = absolute_name.rpartition('.')
        parent_module = import_module(parent_name)
        path = parent_module.__spec__.submodule_search_locations
    for finder in sys.meta_path:
        spec = finder.find_spec(absolute_name, path)
        if spec is not None:
            break
    else:
        msg = f'No module named {absolute_name!r}'
        raise ModuleNotFoundError(msg, name=absolute_name)
    module = importlib.util.module_from_spec(spec)
    sys.modules[absolute_name] = module
    spec.loader.exec_module(module)
    if path is not None:
        setattr(parent_module, child_name, module)
    return module

See also