isinstance（）意外返回False

Question

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

当客户端无法连接时，它会抛出一个urllib3.exceptions.MaxRetryError异常，因此我从以下内容开始：

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)

但这完全失败了；它的行为就像没有任何except声明，并且可以解决：

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',))

我以为也许我不像我想象的那样理解继承，所以我将上述内容替换为：

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

以相同的方式失败。为了弄清楚发生了什么，我添加了一个except包罗万象并调用pdb：

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

从pdb提示符处，我们可以看到：

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

…看起来不错，MRO也一样：

(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'>)

但是尽管如此：

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

并且所有路径看起来都是合理的：

(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'

那么…这里到底发生了什么？

更新资料

这是完整的堆栈跟踪：

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

您的代码对requests程序包具有间接依赖关系，并且requests程序包具有名为的奇怪子模块requests.packages。它曾经包含来自多个依赖项（包括）的复制源代码urllib3，但他们停止这样做。他们想保持requests.packages向后兼容性，所以现在他们做的事情很奇怪。

urllib3。根据requests版本的不同，它可能还会设置许多其他sys.modules`条目。例如，从请求2.18.4开始，源代码会

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，

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不良。如果某些代码尝试执行该操作，import requests.packages.urllib3.exceptions而Python找不到sys.modules['requests.packages.urllib3.exceptions']条目，则Python将
重新创建
该urllib3.exceptions模块并进行设置urllib3.exceptions，并设置sys.modules['requests.packages.urllib3.exceptions']到新模块（但不会涉及sys.modules['urllib3.exceptions']。这将生成所涉及类的新副本，从而导致您的错误）。

早在5月份就报告了一个具有相同原因的相关问题，导致了2.18.4中显示的新代码。2.18.4不应引起您所看到的特定问题，但是它仍然很脆弱，因为如果urllib3在用requests.packages拧紧时尚未加载的任何子模块sys.modules，这些子模块将表现出与您今天看到的相同的问题。