Python 使用 importlib 从包目录导入模块

Question

我正在尝试使用 importlib 动态导入 PySide2，因为使用 import 静态导入 PySide2 对我的应用程序来说是不够的。我需要 importlib 因为最后它将与 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。

我已经复制了用 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 "PySide2" 目录出现在我的源目录中时，我想改用它。

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到看到它存在):

$ 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

我不明白为什么在 sys.modules.

中显示 "name 'PySide2' is not define"

Answer 1

从 documentation 开始，当找不到本地或全局名称时会引发 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
使用指向 import foo 的实际模块对象的变量名称更新全局字典，当 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2个步骤，你只需要添加：

PySide2 = module

Python 使用 importlib 从包目录导入模块

Python use importlib to import a module from a package directory

python

import

module

dynamic

python-importlib