urllib3 version conflict

ssladapter.py makes an attempt to import urllib3 from requests and if it fails, attempts to import urllib3 directly – see https://github.com/docker/docker-py/blob/453964466741a1c85fc420c8b40fb5710f40b017/docker/transport/ssladapter.py#L10-L13. This may result in an older version of urllib3 being used at runtime. For example, the line at https://github.com/docker/docker-py/blob/453964466741a1c85fc420c8b40fb5710f40b017/docker/transport/ssladapter.py#L22 fails for versions of urllib3 before version 1.8 with the following exception:

AttributeError: 'module' object has no attribute 'connection'

Proposal for resolution: Specify urllib3>=1.8 in requirements.txt and setup.py, import directly from urllib3 rather than import from the version bundled w/ requests.

[shin-]

This honestly is an issue with Ubuntu and its stubbornness with messing with the packaging / bundling of certain Python libraries.

I won’t add urllib3 to our requirements.txt because urllib3 is not a requirement of the docker SDK - requests is.

If you decide (or your OS decides) to use older versions of libraries than the ones we indicate and test our software with, you have to accept the consequences of those choices and the extra work it might entail. We have made reasonable concessions to support a wide range of setups (i.e. fallback on urllib3 import when requests.packages.urllib3 is unfortunately absent), but none that would compromise the quality of the software for the majority of users.

You may solve this issue by using virtualenv, or using a more recent version of Ubuntu.

[oxtopus]

Thanks for looking into this and I appreciate the consideration. I understand it’s a bit of a corner case, but the reason I brought it up is wrapping the requests import in a try...except ImportError block produces a bit of a red herring, resulting in some unnecessary confusion.

In my case, I’m not using docker-py, but the official docker formula attempts to install it by default. At the very least, this suggestion is informed by the maxim Explicit is better than implicit.