Alan Isaac <ai****@american.eduwrote:
"Alex Martelli" <al***@mac.comwrote in message
news:1h**************************@mac.com...
If you're running test1.py as your main module, then it's not part of a
package, so the relative import should indeed fail as you mention.
So if I understand you,
in a package, any module that I wish
to make available for execution as a script
(in the usual way, with a main function)
cannot have any relative imports.
Is this right? What is the reason for
this restriction? (And where is it
documented?)
The most up-to-date documentation for import and from statements is at
<http://docs.python.org/dev/ref/import.htmlbut it's still somewhat
incomplete -- it gives the grammar for relative imports, but does not
explain its semantics, nor, for that matter, any of the semantics of
pakages. The discussions about relative imports in particular are
recorded as PEP 328, while an old essay about the semantics of packages
is recorded at a link give on the docs page I mentioned.
Very simply, PEP 328 explains:
"""
Relative Imports and __name__
Relative imports use a module's __name__ attribute to determine that
module's position in the package hierarchy. If the module's name does
not contain any package information (e.g. it is set to '__main__') then
relative imports are resolved as if the module were a top level module,
regardless of where the module is actually located on the file system.
"""
and points to four discussion threads on python-dev which, after much
give and take, led to Guido picking these semantics.
To me, it makes sense: if a module is top-level, and thus not part of a
package (and __main__ in particular is always in that state), then
saying "import from the current package" has no well defined meaning,
because there IS no "current package". Using __name__ rather than
__file__, in turn, makes a lot of sense, because a package's _logical_
structure is defined by its __path__, and need not coincide with any
_physical_ arrangement of directories.
If you have a better and sharper idea about how relative imports should
work in toplevel modules (those whose __name__ indicates they have NOT
been imported as part of a package, including __main__), feel free to
make a case for it on python-dev (python-list is fine for preliminary
discussions and brainstorming, but nothing will happen about any idea
until and unless it's taken to python-dev, survives the scathing barrage
of objections that strongly characterizes that mailing list, and finally
manages to convince Guido:-).
Alex
