swig/Examples/python/import_packages/from_init1/README
Paweł Tomulik 5562deec62 Fixed SF bug #1297 (Python imports)
This changeset resolves several issues related to python imports.
For example, it's possible now to import modules having same module
names, but belonging to different packages.

From the user's viewpoint, this patch gives a little bit more control on
import directives generated by swig. The user may choose to use relative
or absolute imports (docs are provided in separate PR).

Some details:
  - we (still) generate import directives in form 'import a.b.c' which
    corresponds to absolute imports in python3 and (the only available)
    ambiguous one in python2.
  - added -relativeimport option to use explicit relative import syntax
    (python3),

Tests are under Examples/python, these are in fact regression tests but
with the current swig testing framework it seems to be impossible to put
appropriate tests under test-suite.

Closes #7
2013-12-24 17:22:25 +00:00

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This example tests the %import directive and python import from __init__.py.
This case is not correctly handled by swig 2.
The issue was reported as Source Forge bug #1297 and later as GitHub issue #7.
Use 'python runme.py' to run a test.
Overview:
---------
The example defines 2 different extension modules--each wrapping a separate C++
class.
pyX/pkg2/foo.i - Pkg2_Foo class
pyX/pkg2/bar.i - Pkg2_Bar class derived from Pkg2_Foo
and the package pyX.pkg2 has:
pyX/pkg2/__init__.py - which imports something from "bar" module (we
import Pkg2_Bar class, but it is not the clue,
the clue is the 'from' keyword)
For example with python2.x the py2/pkg2/__init__.py imports Pkg2_Bar class
as follows
from bar import Pkg2_Bar # [1]
Such cases doesn't work when fully qualified python module names are used by
swig (swig 2.0.10, e.g.) to generate python import directives (SF bug #1297).
The generated file "py2/pkg2/bar.py" has following lines:
import py2.pkg2.foo # [2]
class Pkg2_Bar(py2.pkg2.foo.Pkg2_Foo): # [3]
but it's not possible to import anything from py2.pkg2 subpackage, e.g.
import py2.pkg2
fails with the following exception:
Traceback (most recent call last):
File "runme.py", line 3, in <module>
import py2.pkg2
File "py2/pkg2/__init__.py", line 7, in <module>
from .bar import Pkg2_Bar
File "py2/pkg2/bar.py", line 71, in <module>
class Pkg2_Bar(py2.pkg2.foo.Pkg2_Foo):
AttributeError: 'module' object has no attribute 'pkg2'
It seems like during the import [1], the sub-package pkg2 is not yet fully
initialized, so py2.pkg2 is not known. The above exception is raised at
line [3]. The problem disappears, for example, if we force swig to use relative
package names.
If everything works well, the package py2.pkg2 shall load properly.
Unix:
-----
- Run make
- Run the test as described above