Re: [Distutils] [Numpy-discussion] Proposal: stop supporting 'setup.py install'; start requiring 'pip install .' instead

On Sun, Nov 8, 2015 at 12:52 PM, Paul Moore wrote:

On 8 November 2015 at 17:42, Nathaniel Smith wrote:

...

I'm not sure exactly what's at stake in this terminological/ontological debate, but it certainly is fairly common for developers to have conversations like "thanks for reporting that issue, I think it's fixed in master but can't reproduce myself so can you try 'pip install https://github.com/pydata/patsy/archive/master.zip' and report back whether it helps?"

Well, reviewing this scenario is probably much more useful than the endless terminology debates that I seem to be forever starting, so thanks for stopping me!

It seems to me that in this situation, optimising rebuild times probably isn't too important. The user is likely to only be building once or twice, so reusing object files from a previous build isn't likely to be a killer benefit.

Sure. And there's no reasonable way to optimize rebuild times anyway when the input is a remote URL -- it's only when the input is an on-disk directory that worrying about incremental builds even makes sense.

However, if the user does as you asked here, they'd likely be pretty surprised (and it'd be a nasty situation for you to debug) if pip didn't install what the user asked. In all honesty, You could argue that this implies that pip should unconditionally install files specified on the command line,

Yes, that is what I do argue :-)

but I'd suggest that you should actually be asking the user to run 'pip install --ignore-installed https://github.com/pydata/patsy/archive/master.zip'. That avoids any risk that whatever the user has currently installed could mess things up, and is explicit that it's doing so (and equally, it's explicit that it'll overwrite the currently installed version, which the user might not want to do in his main environment).

Problem 1 is that I don't actually know what --ignore-installed does. My first guess is that it would cause pip to skip uninstalling packages before upgrading them, resulting in an inconsistent/corrupt environment. (No, this doesn't sound like particularly useful behavior to me either, but most operations/switches in pip have semantics that are somewhat skewed from what I would consider intuitive, so who knows. It's right next to --no-deps in the --help output, and --no-deps is literally a "please give me an inconsistent/corrupt environment" switch, so it's totally plausible that --ignore-installed is intended for similarly ill-conceived uses.) Or maybe it causes pip to pretend that the environment is totally empty when picking the set of (package, version) tuples to install, triggering upgrades of dependent packages? I would actually guess both of those before guessing that it means "please actually install the thing I asked you to install, but otherwise act normally", and as of right now I still actually have no idea which of these is correct (if any). AFAICT there aren't any docs -- maybe I'm just failing to search properly. Problem 2 is that even if --ignore-installed does do the appropriate thing, and even if there is some way for me to figure this out, then it will still inevitably happen that 1 in 10 times I will forget to mention it, not notice that I have forgotten to mention it, and the user will not realize that nothing has happened, and just report that "they installed the new version but they still get the same error", and then I spend hours tearing out my hair trying to figure out why not (because I "know" that they actually installed the new version). If you want to optimize your UI to frustrate people and waste their time, then a really impressively good technique is to include a special switch that usually does nothing, but every once in a while is necessary, and if you forget it then the computer and the user's mental model will get totally out of sync. Otherwise, though... :-/

Maybe you could argue that you want --ignore-installed to be the default (probably only when a file is specified rather than a requirement, assuming that distinguishing between a file and a requirement is practical). But if we did that, we'd still need a --dont-ignore-installed flag to restore the current behaviour. For example, because Christoph Gohlke's builds must be manually downloaded, I find it's quite common to download a wheel from his site and "pip install" it in a number of environments, with the meaning "only if it'd be an upgrade to whatever is currently installed".

Sure, I have no objection to a pip install --only-if-upgrade flag. -n -- Nathaniel J. Smith -- http://vorpus.org