isinstance()意外返回False

Question

我正在使用kubernetes python客户端。如果当我的代码启动时kubernetes不可用，我想重试连接。

当客户端无法连接时，它会抛出似乎是urllib3.exceptions.MaxRetryError异常，因此我从如下内容开始：

import time
import urllib3

import kubernetes

kubernetes.config.load_kube_config()
api = kubernetes.client.CoreV1Api()

while True:
    try:
        w = kubernetes.watch.Watch()
        for event in w.stream(api.list_pod_for_all_namespaces):
            print event
    except urllib3.exceptions.HTTPError:
        print('retrying in 1 second')
        time.sleep(1)

但是，这完全失败了；它的表现就像没有except语句一样，并且使用：

urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='192.168.122.140', port=8443): Max retries exceeded with url: /api/v1/pods?watch=True (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x2743110>: Failed to establish a new connection: [Errno 111] Connection refused',))

我想，也许我不像我想的那样理解继承，所以我用以下内容代替了上面的内容：

except urllib3.exceptions.MaxRetryError:
    print('retrying in 1 second')
    time.sleep(1)

以同样的方式失败。为了弄清到底发生了什么，我添加了一个catch except并调用了pdb：

except Exception as err:
    import pdb; pdb.set_trace()

从pdb提示符中，我们可以看到：

(Pdb) type(err)
<class 'urllib3.exceptions.MaxRetryError'>

...which看起来很好，mro也是这样：

(Pdb) import inspect
(Pdb) inspect.getmro(err.__class__)
(<class 'urllib3.exceptions.MaxRetryError'>, <class 'urllib3.exceptions.RequestError'>, <class 'urllib3.exceptions.PoolError'>, <class 'urllib3.exceptions.HTTPError'>, <type 'exceptions.Exception'>, <type 'exceptions.BaseException'>, <type 'object'>)

但尽管如此：

(Pdb) isinstance(err, urllib3.exceptions.MaxRetryError)
False

所有的道路看起来都是合理的：

(Pdb) urllib3.__file__
'/usr/lib/python2.7/site-packages/urllib3/__init__.pyc'
(Pdb) kubernetes.client.rest.urllib3.__file__
'/usr/lib/python2.7/site-packages/urllib3/__init__.pyc'

So...what这到底是怎么回事？

更新

下面是完整的堆栈跟踪：

Traceback (most recent call last):
  File "testkube.py", line 13, in <module>
    for event in w.stream(api.list_pod_for_all_namespaces):
  File "/usr/lib/python2.7/site-packages/kubernetes/watch/watch.py", line 116, in stream
    resp = func(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/kubernetes/client/apis/core_v1_api.py", line 14368, in list_pod_for_all_namespaces
    (data) = self.list_pod_for_all_namespaces_with_http_info(**kwargs)
  File "/usr/lib/python2.7/site-packages/kubernetes/client/apis/core_v1_api.py", line 14464, in list_pod_for_all_namespaces_with_http_info
    collection_formats=collection_formats)
  File "/usr/lib/python2.7/site-packages/kubernetes/client/api_client.py", line 335, in call_api
    _preload_content, _request_timeout)
  File "/usr/lib/python2.7/site-packages/kubernetes/client/api_client.py", line 148, in __call_api
    _request_timeout=_request_timeout)
  File "/usr/lib/python2.7/site-packages/kubernetes/client/api_client.py", line 371, in request
    headers=headers)
  File "/usr/lib/python2.7/site-packages/kubernetes/client/rest.py", line 250, in GET
    query_params=query_params)
  File "/usr/lib/python2.7/site-packages/kubernetes/client/rest.py", line 223, in request
    headers=headers)
  File "/usr/lib/python2.7/site-packages/urllib3/request.py", line 66, in request
    **urlopen_kw)
  File "/usr/lib/python2.7/site-packages/urllib3/request.py", line 87, in request_encode_url
    return self.urlopen(method, url, **extra_kw)
  File "/usr/lib/python2.7/site-packages/urllib3/poolmanager.py", line 321, in urlopen
    response = conn.urlopen(method, u.request_uri, **kw)
  File "/usr/lib/python2.7/site-packages/urllib3/connectionpool.py", line 668, in urlopen
    **response_kw)
  File "/usr/lib/python2.7/site-packages/urllib3/connectionpool.py", line 668, in urlopen
    **response_kw)
  File "/usr/lib/python2.7/site-packages/urllib3/connectionpool.py", line 668, in urlopen
    **response_kw)
  File "/usr/lib/python2.7/site-packages/urllib3/connectionpool.py", line 639, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "/usr/lib/python2.7/site-packages/urllib3/util/retry.py", line 388, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='192.168.122.140', port=8443): Max retries exceeded with url: /api/v1/pods?watch=True (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x3d16110>: Failed to establish a new connection: [Errno 111] Connection refused',))

Answer 1

您的代码间接依赖于requests包，而requests包有一个名为requests.packages的奇怪子模块。这曾经包含从许多依赖项(包括urllib3 )复制的源代码，但是他们停止了这样做。不过，他们希望保持requests.packages的向后兼容性，所以现在他们正在做一些奇怪的事情。

它现在没有导入requests.packages (包括urllib3源代码的完整副本)，而是导入urllib3并设置sys.modules['requests.packages.urllib3'] = urllib3。根据requests版本的不同，它也可以设置许多其他的sys.modules条目；例如，对于请求2.18.4，源代码可以设置

for package in ('urllib3', 'idna', 'chardet'):
    locals()[package] = __import__(package)
    # This traversal is apparently necessary such that the identities are
    # preserved (requests.packages.urllib3.* is urllib3.*)
    for mod in list(sys.modules):
        if mod == package or mod.startswith(package + '.'):
            sys.modules['requests.packages.' + mod] = sys.modules[mod]

但在2.17.0中，它确实

import urllib3
sys.modules['requests.packages.urllib3'] = urllib3

import idna
sys.modules['requests.packages.idna'] = idna

import chardet
sys.modules['requests.packages.chardet'] = chardet

此代码与导入包的子模块交互很差。如果一些代码尝试执行import requests.packages.urllib3.exceptions，而Python没有找到sys.modules['requests.packages.urllib3.exceptions']条目，Python将重新创建urllib3.exceptions模块，并将urllib3.exceptions和sys.modules['requests.packages.urllib3.exceptions']设置为新模块(但不会触及sys.modules['urllib3.exceptions'] )。这将生成涉及的类的新副本，从而导致您的错误。

同样原因的一个相关问题是5月份的已报告，导致了2.18.4中所示的新代码。2.18.4不应该引起您所看到的特定问题，但是它仍然是脆弱的，因为如果urllib3的任何子模块在使用sys.modules的requests.packages螺丝时还没有加载，那么这些子模块将显示出与现在相同的问题。