Python 使用 importlib 从包目录中导入模块

Question

我正在尝试使用 importlib 动态导入 PySide2，因为使用 import 静态导入对于我的应用程序来说是不够的。我需要 importlib，因为最终它将与 pyinstaller 一起使用来创建一个可以动态导入 PySide2 的可执行文件，而不仅仅是从单个可执行文件中导入。

我已经复制了一个用 pip 下载的整个 PySide2 包目录。这个 PySide2 版本比我默认使用的版本旧，当我的源目录中存在“PySide2”目录时，我想使用它。

根据this post 中的答案，我有以下代码来执行导入：

import os, sys
print("Import test")
if os.path.isdir('./PySide2/'):
    print('Importing local PySide2')
    import importlib.util

    MODULE_PATH = "./PySide2/__init__.py"
    MODULE_NAME = "PySide2"

    spec = importlib.util.spec_from_file_location(MODULE_NAME, MODULE_PATH)
    print("spec.name is " + str(spec.name))
    module = importlib.util.module_from_spec(spec)
    sys.modules[spec.name] = module 
    print(sys.modules)
    spec.loader.exec_module(module)

    print(PySide2.__version__)
else:
    print('Importing system PySide2')
    import PySide2
    print(PySide2.__version__)

但是当我运行它时，我得到NameError: name 'PySide2' is not defined，即使我在 sys.modules 中看到 PySide2 存在（在下面的输出中一直向右滚动以查看它存在）：

$ python importTest.py
Import test
Importing local PySide2
spec.name is PySide2
{'sys': <module 'sys' (built-in)>, 'builtins': <module 'builtins' (built-in)>, '_frozen_importlib': <module 'importlib._bootstrap' (frozen)>, '_imp': <module '_imp' (built-in)>, '_thread': <module '_thread' (built-in)>, '_warnings': <module '_warnings' (built-in)>, '_weakref': <module '_weakref' (built-in)>, 'zipimport': <module 'zipimport' (built-in)>, '_frozen_importlib_external': <module 'importlib._bootstrap_external' (frozen)>, '_io': <module 'io' (built-in)>, 'marshal': <module 'marshal' (built-in)>, 'posix': <module 'posix' (built-in)>, 'encodings': <module 'encodings' from '/usr/lib/python3.7/encodings/__init__.py'>, 'codecs': <module 'codecs' from '/usr/lib/python3.7/codecs.py'>, '_codecs': <module '_codecs' (built-in)>, 'encodings.aliases': <module 'encodings.aliases' from '/usr/lib/python3.7/encodings/aliases.py'>, 'encodings.utf_8': <module 'encodings.utf_8' from '/usr/lib/python3.7/encodings/utf_8.py'>, '_signal': <module '_signal' (built-in)>, '__main__': <module '__main__' from 'importTest.py'>, 'encodings.latin_1': <module 'encodings.latin_1' from '/usr/lib/python3.7/encodings/latin_1.py'>, 'io': <module 'io' from '/usr/lib/python3.7/io.py'>, 'abc': <module 'abc' from '/usr/lib/python3.7/abc.py'>, '_abc': <module '_abc' (built-in)>, 'site': <module 'site' from '/usr/lib/python3.7/site.py'>, 'os': <module 'os' from '/usr/lib/python3.7/os.py'>, 'stat': <module 'stat' from '/usr/lib/python3.7/stat.py'>, '_stat': <module '_stat' (built-in)>, 'posixpath': <module 'posixpath' from '/usr/lib/python3.7/posixpath.py'>, 'genericpath': <module 'genericpath' from '/usr/lib/python3.7/genericpath.py'>, 'os.path': <module 'posixpath' from '/usr/lib/python3.7/posixpath.py'>, '_collections_abc': <module '_collections_abc' from '/usr/lib/python3.7/_collections_abc.py'>, '_sitebuiltins': <module '_sitebuiltins' from '/usr/lib/python3.7/_sitebuiltins.py'>, 'sitecustomize': <module 'sitecustomize' from '/usr/lib/python3.7/sitecustomize.py'>, 'importlib': <module 'importlib' from '/usr/lib/python3.7/importlib/__init__.py'>, 'importlib._bootstrap': <module 'importlib._bootstrap' (frozen)>, 'importlib._bootstrap_external': <module 'importlib._bootstrap_external' (frozen)>, 'types': <module 'types' from '/usr/lib/python3.7/types.py'>, 'warnings': <module 'warnings' from '/usr/lib/python3.7/warnings.py'>, 'importlib.util': <module 'importlib.util' from '/usr/lib/python3.7/importlib/util.py'>, 'importlib.abc': <module 'importlib.abc' from '/usr/lib/python3.7/importlib/abc.py'>, 'importlib.machinery': <module 'importlib.machinery' from '/usr/lib/python3.7/importlib/machinery.py'>, 'contextlib': <module 'contextlib' from '/usr/lib/python3.7/contextlib.py'>, 'collections': <module 'collections' from '/usr/lib/python3.7/collections/__init__.py'>, 'operator': <module 'operator' from '/usr/lib/python3.7/operator.py'>, '_operator': <module '_operator' (built-in)>, 'keyword': <module 'keyword' from '/usr/lib/python3.7/keyword.py'>, 'heapq': <module 'heapq' from '/usr/lib/python3.7/heapq.py'>, '_heapq': <module '_heapq' (built-in)>, 'itertools': <module 'itertools' (built-in)>, 'reprlib': <module 'reprlib' from '/usr/lib/python3.7/reprlib.py'>, '_collections': <module '_collections' (built-in)>, 'functools': <module 'functools' from '/usr/lib/python3.7/functools.py'>, '_functools': <module '_functools' (built-in)>, 'PySide2': <module 'PySide2' from './PySide2/__init__.py'>}
Traceback (most recent call last):
  File "importTest.py", line 17, in <module>
    print(PySide2.__version__)
NameError: name 'PySide2' is not defined

当它出现在 sys.modules 中时，我不明白为什么它说“名称 'PySide2' 未定义”。

Answer 1

从documentation，当找不到本地或全局名称时引发NameError。

对于标准导入语句， 它会做以下事情：

• 查找并加载模块
• 更新 sys.modules
• 用指向import foo的实际模块对象的变量名更新全局dict，当它是import * from something时更新多个变量（同时检查模块的__all__）

这里你已经手动完成了前两个步骤，你只需要添加：

PySide2 = module