M2Crypto, if imported, globally monkeypatches urllib in incompatible manner (no error handling)

[Mekk]

The file:
  /usr/lib/python2.7/dist-packages/M2Crypto/m2urllib.py
ends with the following snippet (where URLOpener is result of "from urrlib import *")
  # Minor brain surgery.
  URLopener.open_https = open_https

This globally replaces urrlib.URLOpener.open_https method with incompatible version.

The critical difference is in (lack of) error handling. While standard urllib version ends with analysis of reply status and calls to self.http_error (which further calls methods like http_error_401 and in the end for example handles authorization errors), M2Crypto version blindly returns obtained payload whatever the status is. Final part of M2Crypto's open_https is:
    resp = h.getresponse()
    fp = resp.fp
    return addinfourl(fp, resp.msg, "https:" + url)
while urllib ends with
    errcode, errmsg, headers = h.getreply()
    # … and plenty of lines follow where addinfourl is used only if 200 <= errcode < 300,
    # otherwise self.http_error is called to handle the error

(there are also differences in preparation phase, I didn't analyse them)

~~~~~~~~~~

In my practice I have an app which subclasses urllib.FancyURLOpener to provide customized error handling (in fact some custom ways of secrets loading). After some update of some dependency of dependency of dependency¹ my code use, M2Crypto appeared in the process and broke all those callbacks by just never calling them.

¹ For curious: I got M2Crypto in process because keyring library (which I actually use) for some reason imported keyrings.alt.Google (which I don't use but keyring iterates over available backends and attempts to import them all) which imported gdata which imported gdata.tlslite which imported M2Crypto.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: python-m2crypto 0.27.0-5
ProcVersionSignature: Ubuntu 4.15.0-55.60-lowlatency 4.15.18
Uname: Linux 4.15.0-55-lowlatency x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.7
Architecture: amd64
CurrentDesktop: KDE
Date: Wed Sep 4 11:52:39 2019
EcryptfsInUse: Yes
InstallationDate: Installed on 2013-02-18 (2389 days ago)
InstallationMedia: Ubuntu-Server 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120817.3)
SourcePackage: m2crypto
UpgradeStatus: Upgraded to bionic on 2018-04-11 (511 days ago)