[Python-Dev] Relative import (original) (raw)

Tim Peters tim.one at comcast.net
Wed Dec 17 22:06:13 EST 2003

[Barry]

... I'll just note that where the current status quo trips /me/ up most is when I accidentally have a local module with the same name as a global module, and then I write an import statement expecting to get the standard library module, but end up getting the local module.

Indeed, this is common on c.l.py and the Tutor lists, with a twist: someone writes a module in their current directory, with a name like random.py, and then "Python breaks mysteriously all over the place", because every import of random ends up with something utterly unexpected. For some reason, "random.py" seems most often to be the actual name used in these cases.

Possibly related: I remember pissing away a day a year or so ago trying to track down a segfault in a Zope test that happened only when I ran the test on my McLean box. In the end, it turned out that the test in question was (after untangling the usual layers of Zopish indirection <wink/grrrr>) deliberately trying to import a module that didn't exist, with an oddball name. It just so happened that somebody had whittled down a segfaulting Python program and uploaded it to SourceForge, with the very same oddball name. I had downloaded that program into my Python build directory, and Zope kept provoking its segfault as a side effect of (unintentionally!) importing it.

In large part, I've come to loathe imports -- I never have the foggiest idea how they're going to get satisfied in code I didn't write, and especially in code that plays every trick in (and out) of the book to hide what it's really doing with sys.path mutations, import hooks, poking stuff by magic into sys.modules via well-hidden side effects in scattered init.py files, ... it makes Java's rigid, wordy, explicit import scheme look very attractive some days. That you can't trick that into doing arbitrarily unexpected things by magic at runtime isn't entirely a bad thing .

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