Thursday, May 22, 2014

[Python, Windows] `pkg_resources not found` issue? Check your permissions.

It's been a long time coming ...

I've been meaning to post about this for awhile, and I've seen numerous SO Q&A regarding this issue, while I was trying to resolve it myself.

How embarrassing!

Nothing is more embarrassing than when you are demo-ing some software, and it fails in front of the user in cryptic fashion. Especially if the user is not tech savvy (read: scared of command line) or already disinclined (for some truly bizarre reason) to coding already, this is a real stumbling block and a major put-off. Well that's what happened at my big unveiling, when releasing new analytical tools for my group to use; they logged in to the servers I had setup, trusting me blindly only to be thwarted by this inexplicable error that seemed to substantiate every fear and preconceived misconception they had just below the surface been expecting and had now been confirmed. This was of course the moment where I swoop in and show them that the fix was trivially not only confirming their trust in me, the computer geek, but also reaffirming their faith in their own ability to utilize this fantastical new gizmotron we call the 'puter. But alas, I was completely at a loss, and evidentally so was everyone else in the universe because where ever I did see this issue, the solution was inevitably and misguidedly to re-install Setuptools, the package responsible for `pkg_resources()`.

Redux

Well, I finally had some time to check out the source of this issue. Luckily I have a coworker who actually gets excited about computing. You would think this was the norm at a heavily scientific engineering group. And although he may be a geek, he is mostly a hands on engineer. But he is also a genius who uses whatever the best tools on hand are to get whatever he needs done. And he's a wicked fast learner. I have a workstation with quite a bit of power, and I offered to share it with him so that he could bring it to bear on a particular challenging mixed-integer binary linear programming problem he was working on (that he completely taught himself). Bam! We immediately hit the `pkg_resources() not found` issue.

Interlude

I should mention that we do not work on our computers as admins, but instead using Windows 7 and UAC, elevate our credentials when necessary. It's not as graceful as `sudo` on Mac or Linux, but I think it gives us flexibility yet a smidge more safety.

Eureka!

So I had an inkling that it might be a permissions issue, and sure enough, I had been using pip as a normal user to install all of my pure Python packages. This meant that I was the owner of those files, and even though everyone in my domain had read and execute rights, that still wasn't enough for `pkg_resources()` to function. Not surprising because usually, unless you are using a virtualenv or a .local site-packages folder, you always have to use `sudo` to pip packages on Mac or Linux.

Solution

Probably other ways I could have solved this, but I changed permissions of all of the packages and scripts to `SYSTEM`, and voila, the issue was solved, without re-installing a thing.

OK, I did actually update Setuptools while logged in as the other user, since so many SO posts were suggesting this, and it gave me a clue to what the issue was, especially when it still didn't solve the issue for a couple of other packages that still could not be imported, or only functioned partially.

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