python - 使用 pytest 测试 __init__.py 中可选依赖项的导入:Python 3.5 /3.6 的行为不同
问题描述
我有一个适用于 python 3.5 和 3.6 的包,它具有可选的依赖项,我想要在任一版本上运行的测试(pytest)。
我在下面做了一个简化的示例,由两个文件组成,一个简单__init__.py
的可选包“requests”(只是一个示例)被导入,并设置了一个标志来指示请求的可用性。
mypackage/
├── mypackage
│ └── __init__.py
└── test_init.py
__init__.py
文件内容:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
requests_available = True
try:
import requests
except ImportError:
requests_available = False
test_init.py
文件内容:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import pytest, sys
def test_requests_missing(monkeypatch):
import mypackage
import copy
fakesysmodules = copy.copy(sys.modules)
fakesysmodules["requests"] = None
monkeypatch.delitem(sys.modules,"requests")
monkeypatch.setattr("sys.modules", fakesysmodules)
from importlib import reload
reload(mypackage)
assert mypackage.requests_available == False
if __name__ == '__main__':
pytest.main([__file__, "-vv", "-s"])
该test_requests_missing
测试适用于 Python 3.6.5:
runfile('/home/bjorn/python_packages/mypackage/test_init.py', wdir='/home/bjorn/python_packages/mypackage')
============================= test session starts ==============================
platform linux -- Python 3.6.5, pytest-3.6.1, py-1.5.2, pluggy-0.6.0 -- /home/bjorn/anaconda3/envs/bjorn36/bin/python
cachedir: .pytest_cache
rootdir: /home/bjorn/python_packages/mypackage, inifile:
plugins: requests-mock-1.5.0, mock-1.10.0, cov-2.5.1, nbval-0.9.0, hypothesis-3.38.5
collecting ... collected 1 item
test_init.py::test_requests_missing PASSED
=========================== 1 passed in 0.02 seconds ===========================
但不是在 Python 3.5.4 上:
runfile('/home/bjorn/python_packages/mypackage/test_init.py', wdir='/home/bjorn/python_packages/mypackage')
========================================================= test session starts ==========================================================
platform linux -- Python 3.5.4, pytest-3.6.1, py-1.5.2, pluggy-0.6.0 -- /home/bjorn/anaconda3/envs/bjorn35/bin/python
cachedir: .pytest_cache
rootdir: /home/bjorn/python_packages/mypackage, inifile:
plugins: requests-mock-1.5.0, mock-1.10.0, cov-2.5.1, nbval-0.9.1, hypothesis-3.38.5
collecting ... collected 1 item
test_init.py::test_requests_missing FAILED
=============================================================== FAILURES ===============================================================
________________________________________________________ test_requests_missing _________________________________________________________
monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7f9a2953acc0>
def test_requests_missing(monkeypatch):
import mypackage
import copy
fakesysmodules = copy.copy(sys.modules)
fakesysmodules["requests"] = None
monkeypatch.delitem(sys.modules,"requests")
monkeypatch.setattr("sys.modules", fakesysmodules)
from importlib import reload
> reload(mypackage)
test_init.py:13:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
../../anaconda3/envs/bjorn35/lib/python3.5/importlib/__init__.py:166: in reload
_bootstrap._exec(spec, module)
<frozen importlib._bootstrap>:626: in _exec
???
<frozen importlib._bootstrap_external>:697: in exec_module
???
<frozen importlib._bootstrap>:222: in _call_with_frames_removed
???
mypackage/__init__.py:8: in <module>
import requests
../../anaconda3/envs/bjorn35/lib/python3.5/site-packages/requests/__init__.py:97: in <module>
from . import utils
.... VERY LONG OUTPUT ....
from . import utils
../../anaconda3/envs/bjorn35/lib/python3.5/site-packages/requests/__init__.py:97: in <module>
from . import utils
<frozen importlib._bootstrap>:968: in _find_and_load
???
<frozen importlib._bootstrap>:953: in _find_and_load_unlocked
???
<frozen importlib._bootstrap>:896: in _find_spec
???
<frozen importlib._bootstrap_external>:1171: in find_spec
???
<frozen importlib._bootstrap_external>:1145: in _get_spec
???
<frozen importlib._bootstrap_external>:1273: in find_spec
???
<frozen importlib._bootstrap_external>:1245: in _get_spec
???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
name = 'requests', location = '/home/bjorn/anaconda3/envs/bjorn35/lib/python3.5/site-packages/requests/__init__.py'
> ???
E RecursionError: maximum recursion depth exceeded
<frozen importlib._bootstrap_external>:575: RecursionError
======================================================= 1 failed in 2.01 seconds =======================================================
我有两个问题:
为什么我会看到这种差异?相关软件包在 3.5 和 3.6 上似乎具有相同的版本。
有没有更好的方法来做我想做的事?我现在的代码是从网上找到的示例拼接在一起的。我试图修补导入机制以避免“重新加载”,但我没有成功。
解决方案
我要么模拟__import__
函数(在语句后面调用的那个import modname
),要么通过添加自定义元路径查找器来自定义导入机制。例子:
改变sys.meta_path
添加一个自定义MetaPathFinder
实现,该实现ImportError
在尝试将任何包导入时引发pkgnames
:
class PackageDiscarder:
def __init__(self):
self.pkgnames = []
def find_spec(self, fullname, path, target=None):
if fullname in self.pkgnames:
raise ImportError()
@pytest.fixture
def no_requests():
sys.modules.pop('requests', None)
d = PackageDiscarder()
d.pkgnames.append('requests')
sys.meta_path.insert(0, d)
yield
sys.meta_path.remove(d)
@pytest.fixture(autouse=True)
def cleanup_imports():
yield
sys.modules.pop('mypackage', None)
def test_requests_available():
import mypackage
assert mypackage.requests_available
@pytest.mark.usefixtures('no_requests2')
def test_requests_missing():
import mypackage
assert not mypackage.requests_available
夹具在调用时no_requests
会改变sys.meta_path
,因此自定义元路径查找器会requests
从可以导入的包名中过滤掉包名(我们不能在任何导入时引发,否则pytest
它会损坏)。cleanup_imports
只是为了确保mypackage
在每次测试中都会重新导入。
嘲笑__import__
import builtins
import sys
import pytest
@pytest.fixture
def no_requests(monkeypatch):
import_orig = builtins.__import__
def mocked_import(name, globals, locals, fromlist, level):
if name == 'requests':
raise ImportError()
return import_orig(name, locals, fromlist, level)
monkeypatch.setattr(builtins, '__import__', mocked_import)
@pytest.fixture(autouse=True)
def cleanup_imports():
yield
sys.modules.pop('mypackage', None)
def test_requests_available():
import mypackage
assert mypackage.requests_available
@pytest.mark.usefixtures('no_requests')
def test_requests_missing():
import mypackage
assert not mypackage.requests_available
在这里,fixtureno_requests
负责__import__
用一个会在import requests
尝试时引发的函数替换该函数,在其余的导入上做得很好。
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