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I recently upgraded versions of pylint, a popular Python style-checker.

It has gone ballistic throughout my code, pointing out places where I import modules in the same package, without specifying the full package path.

The new error message is W0403.

W0403: Relative import %r, should be %r

Used when an import relative to the package directory is detected.


For example, if my packages are structured like this:


and in the sponge package I write:

import icing

instead of

import cake.icing

I will get this error.

While I understand that not all Pylint messages are of equal importance, and I am not afraid to dismiss them, I don't understand why such a practice is considered a poor idea.

I was hoping someone could explain the pitfalls, so I could improve my coding style rather than (as I currently plan to do) turning off this apparently spurious warning.

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up vote 61 down vote accepted

The problem of import icing is that you don't know whether its an absolute import or a relative import. icing could a module in python's path, or a package in the current module. This is quite annoying when a local package has the same name as a python standard library package.

You can do from __future__ import absolute_import which turns off implicit relative imports altogether. It is described, including with this justification about ambiguity, in PEP 328. I believe Python 3000 has implicit relative imports turned off completely.

You still can do relative imports, but you have to do them explicitly, like this:

from . import icing
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+1 especially for the compromise solution, which is probably the way I should go. – Oddthinking Aug 4 '12 at 15:46
Note you can also do import .icing instead of from . import icing – Jack Oct 14 '15 at 1:43
@Jack actually I don't think you can. From this part of PEP328: Relative imports must always use from <> import ; import <> is always absolute. Of course, absolute imports can use from <> import by omitting the leading dots. The reason import .foo is prohibited is because after import XXX.YYY.ZZZ then XXX.YYY.ZZZ is usable in an expression. But .moduleY is not usable in an expression. – A.Wan Nov 13 '15 at 19:50

There are a few good reasons:

  1. Relative imports break easily, when you move a module around.

    Imagine you have a, a foo.baz and a baz module in your package. imports foo.baz, but using a relative import.

    Now, if you were to move to bar, your module suddenly is importing a different baz!

  2. Relative imports are ambiguous. Even without moving around the bar module in the above example, a new developer coming to your project could be forgiven for not realizing that baz is really foo.baz instead of the root-level baz package.

    Absolute imports make it explicit what module is being used. And as import this preaches, explicit is better than implicit.

  3. Python 3 has disabled implicit relative imports altogether; imports are now always interpreted as absolute, meaning that in the above example import baz will always import the top-level module. You will have to use the explicit import syntax instead (from . import baz).

    Porting the example from Python 2 to 3 would thus lead to unexpected problems, using absolute imports now will make your code future-proof.

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+1 for #2 and #3. But #1 must be offset against what happens when the whole directory is moved (e.g. pushed down a level). – Oddthinking Aug 4 '12 at 15:46
@Martijn: about #3. relative imports are NOT disabled in Python 3 at all. Only implicit relative imports are no longer supported with absolute imports being the default and explicit relative imports fully supported with the dot syntax. import .baz will do a relative import alright. And this is available since Python 2.5 with a from __future__ import absolute_import See… and – Philippe Ombredanne Dec 2 '12 at 17:40
@PhilippeOmbredanne: Sorry, I meant implicit relative imports, I'll update. – Martijn Pieters Dec 2 '12 at 17:42

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