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

Guido van Rossum guido at python.org
Wed Dec 17 12:21:57 EST 2003

It's interesting that the "scan upwards on the package name" gets so much support. Back when packages were first introduced, there was a period of time when they were a user-level construct, implemented by a module named "ni" (after the Knights who say "Ni!"). This implemented a full scan upward as the only way. When I reimplemented packages in C, I decided that the scan wasn't used much, and could actually be detrimental (I feared that too many global modules would be accidentally hidden), so I changed it to only looking in only two places: the current package and the toplevel (sys.path).

But at the time it was a given that the import syntax would not be changed. Now that we're entertaining new import syntax, we can do better. How about this for Python 3.0:

import P.Q (1) from P.Q import X (2)

would only look for P in sys.path (I'll call this "absolute import"); and

from ...P.Q import X (3)

would scan for P upwards from the current package. It would require exactly three dots. P.Q of course stands for any dotted name.

Python 2.x would continue to use the current ("ambiguous import") semantics for (1) and (2), but would also support (3) with the Python 3.0 semantics.

It might also be possible to set a "no ambiguous imports" flag to switch to 3.0 semantics for (1) and (2). This might be a future statement in the package's init.py, e.g.

from future import absolute_import

I think this addresses all the concerns I've seen brought up in this thread so far against my original proposal and the variations that were subsequently suggested.

--Guido van Rossum (home page: http://www.python.org/~guido/)

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