http_proxy and https_proxy are common environment variables used cross platform. Currently, urllib.request has support for it, but http.client does not. It probably should.

If support is added to http.client, the handling of proxy environment variables in urllib.request should be factored out and made to be reliant on the changes in http.client (which shouldn't require any new code, only removal).

Given the common usage of the environment variables (as observed by other utilities such as wget and curl), it seems odd to require a user to know about and use the higher level urllib.request API rather than have support for it baked into the lower level http.client API.