Python maximum recursion depth exceeded while calling a Python object （gevent的SSL无限递归错误）的问题解决

报错信息 

源码位置

分析

 很尴尬，完全看不出原因导致这个报错

解决方法

通过删除代码的方式一部一部删除，找到了问题出处

原因是包的顺序出现了问题，把位置互换一下，发现没有报错了，但是很明确的告诉你这两个包没有交互关系，没有依赖关系，但是就是这么神奇，为什么这么神奇

看一个实例解释

vim test.py :

import gevent.monkey
from requests.packages.urllib3.util.ssl_ import create_urllib3_context

# 将monkey patch置于create_urllib3_context引入之前可防止此错误出现。
gevent.monkey.patch_all()

create_urllib3_context()
# output:
# Traceback (most recent call last):
#   File "test.py", line 7, in 
#     create_urllib3_context()
#   File "/usr/lib/python3.6/site-packages/requests/packages/urllib3/util/ssl_.py", line 265, in create_urllib3_context
#     context.options |= options
#   File "/usr/lib/python3.6/ssl.py", line 459, in options
#     super(SSLContext, SSLContext).options.__set__(self, value)
#   File "/usr/lib/python3.6/ssl.py", line 459, in options
#     super(SSLContext, SSLContext).options.__set__(self, value)
#   File "/usr/lib/python3.6/ssl.py", line 459, in options
#     super(SSLContext, SSLContext).options.__set__(self, value)
#   [Previous line repeated 329 more times]
# RecursionError: maximum recursion depth exceeded while calling a Python object

debug

create_urllib3_context代码片段：

...
# requests/packages/urllib3/util/ssl_.py#L250

context = SSLContext(ssl_version or ssl.PROTOCOL_SSLv23)

# Setting the default here, as we may have no ssl module on import
cert_reqs = ssl.CERT_REQUIRED if cert_reqs is None else cert_reqs

if options is None:
    options = 0
    # SSLv2 is easily broken and is considered harmful and dangerous
    options |= OP_NO_SSLv2
    # SSLv3 has several problems and is now dangerous
    options |= OP_NO_SSLv3
    # Disable compression to prevent CRIME attacks for OpenSSL 1.0+
    # (issue #309)
    options |= OP_NO_COMPRESSION

context.options |= options
...

这里的SSLContext的类型为ssl.SSLContext',而不是gevent._ssl3.SSLContext。 即gevent.monkey.patch_all对其没起作用。

查看SSLContext相关代码：

...
# requests/packages/urllib3/util/ssl_.py#L86

try:
    from ssl import SSLContext  # Modern SSL?
except ImportError:
    import sys

    class SSLContext(object):  # Platform-specific: Python 2 & 3.1
        supports_set_ciphers = ((2, 7) <= sys.version_info < (3,) or
                                (3, 2) <= sys.version_info)
...

from ssl import SSLContext是gevent.monkey.patch_all失效的原因所在。 修正为：

import ssl
SSLContext = lambda *args, **kw: ssl.SSLContext(*args, **kw)

当然最好的方案还是在引入gevent库后立即执行monkey patch代码。

analysis

gevent.monkey.patch_all的位置放错导致了create_urllib3_context中的context 的类型为ssl.SSLContext而不是gevent._ssl3.SSLContext。

因此，context.options |= options最后会调用：

# ssl.py#L457

@options.setter
def options(self, value):
    super(SSLContext, SSLContext).options.__set__(self, value)

而不是：

# gevent/_ssl3.py#L67

# In 3.6, these became properties. They want to access the
# property __set__ method in the superclass, and they do so by using
# super(SSLContext, SSLContext). But we rebind SSLContext when we monkey
# patch, which causes infinite recursion.
# https://github.com/python/cpython/commit/328067c468f82e4ec1b5c510a4e84509e010f296
# pylint:disable=no-member
@orig_SSLContext.options.setter
def options(self, value):
    super(orig_SSLContext, orig_SSLContext).options.__set__(self, value)

但是，由于已经调用过了monkey patch代码，故此时的SSLContext实际上是gevent._ssl3.SSLContext， 是ssl.SSLContext的子类。

所以，super(SSLContext, SSLContext).options实际上是super(gevent._ssl3.SSLContext, gevent._ssl3.SSLContext).options， 得到的结果是ssl.SSLContext.options，而不是我们所希望的_ssl._SSLContext.options。

同时，这也造成了无限递归。