动态创建模块的动态导入失败

Question

背景：

• 一个守护进程创建包 p1（例如带有__init__.py 文件的目录）

• 然后在 p1 中创建一个模块 m1。

• 然后守护进程想要从 m1 导入，它的功能（到目前为止一直）。

• 然后在 p1 中创建了一个模块 m2，并且守护进程想要从 m2 导入失败（大多数时候，但不是总是）并出现 ModuleNotFoundError。

查看最后重现问题的小测试脚本。

对我来说非常奇怪的是，在测试脚本中导入 m2 有时会起作用。我想知道是否有一些包内容缓存。如果是这样，如何防止或重新触发它。

（从 sys.modules 中重新加载 p1 和删除 p1 都不起作用）

"""
(python --version: Python 3.8.2)
Dynamic import of dynamically created modules right after creation.
"""

from shutil import rmtree
from os import path, chdir, mkdir, listdir
from importlib import import_module, reload
import sys

# for test-package creation
P1 = 'p1'
INIT = '__init__.py'
INIT_CONTENT = """\
# -*- coding: utf-8 -*-
"""

# for first test-module creation
M1 = 'm1'
M1_CONTENT = """\
# -*- coding: utf-8 -*-

answer = 42
"""

# for second test-module creation
M2 = 'm2'
M2_CONTENT = """\
# -*- coding: utf-8 -*-

hello = 'world'
"""

chdir(path.dirname(__file__))    # make sure we are in the right directory

if path.isdir(P1):
    rmtree(P1)                   # always start off under the same conditions


mkdir(P1)                        # create test-package and first test-module
with open(path.join(P1, INIT), 'w') as f:
    f.write(INIT_CONTENT)
with open(path.join(P1, M1+'.py'), 'w') as f:
    f.write(M1_CONTENT)

# import from the just created module; this worked always so far
from p1.m1 import answer

print(f'{answer=}')

with open(path.join(P1, M2+'.py'), 'w') as f:
    f.write(M2_CONTENT)          # create the second test-module

# check current directory, file and module structure
print('wd-content:', ', '.join(listdir()))
print('p1-content:', ', '.join(listdir(P1)))
print('p1-modlues:', ', '.join([m for m in sys.modules if m.startswith(P1)]))
# reload(sys.modules[P1])  # neither a reload
# del sys.modules[P1]      # nor a deletion of p1 does the trick

# here it most of the time fails (but NOT all the time)
# so far if it fails it fails in all three variants
# so far if it works the 'from ...'-import works already
try:
    from p1.m2 import hello
except ModuleNotFoundError:
    try:
        hello = getattr(import_module(f'{P1}.{M2}'), 'hello')
    except ModuleNotFoundError:
        try:
            hello = getattr(__import__(f'{P1}.{M2}', fromlist=[None]), 'hello')
        except ModuleNotFoundError:
            raise
        else:
            print("__import__-import worked")
    else:
        print("import_module-import worked")
else:
    print("'from ... '-import worked")

print(f'{hello=}')

Answer 1

正如我所想 :) 从 'sys.path_importer_cache' 中删除 'p1' 的条目似乎可以解决问题。