The Scope of Relative Imports

Relative imports can seem a bit perplexing on first encounter, but it helps if you remember a few key points about them:

 

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  • Relative imports apply to imports within packages only. Keep in mind that this feature’s module search path change applies only to import statements within module files located in a package. Normal imports coded outside package files still work exactly as described earlier, automatically searching the directory containing the top-level script first.
  • Relative imports apply to the from statement only. Also remember that this feature’s new syntax applies only to from statements, not import statements. It’s detected by the fact that the module name in a from begins with one or more dots (periods). Module names that contain dots but don’t have a leading dot are package imports, not relative imports.
  • The terminology is ambiguous. Frankly, the terminology used to describe this feature is probably more confusing than it needs to be. Really, all imports are relative to something. Outside a package, imports are still relative to directories listed on the sys.path module search path. As we learned in Chapter 21, this path includes the program’s container directory, PYTHONPATH settings, path file settings, and standard libraries. When working interactively, the program container directory is simply the current working directory.
    For imports made inside packages, 2.6 augments this behavior by searching the package itself first. In the 3.0 model, all that really changes is that normal “absolute” import syntax skips the package directory, but special “relative” import syntax causes it to be searched first and only. When we talk about 3.0 imports as being “absolute,” what we really mean is that they are relative to the directories on sys.path, but not the package itself. Conversely, when we speak of “relative” imports, we mean they are relative to the package directory only. Some sys.path entries could, of course, be absolute or relative paths too. (And I could probably make up something more confusing, but it would be a stretch!)

In other words, “package relative imports” in 3.0 really just boil down to a removal of 2.6’s special search path behavior for packages, along with the addition of special from syntax to explicitly request relative behavior. If you wrote your package imports in the past to not depend on 2.6’s special implicit relative lookup (e.g., by always spelling out full paths from a package root), this change is largely a moot point. If you didn’t, you’ll need to update your package files to use the new from syntax for local package files.