Examples/python/import_packages/from_init3/README

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/pkg3/pkg4/foo.i  - Pkg4_Foo class
     pyX/pkg2/bar.i        - Pkg2_Bar class derived from Pkg4_Foo

and the package pyX.pkg2 has:

     pyX/pkg2/__init__.py  - which imports something from "bar" module

For example with python 2.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 to generate python import directives (SF bug 1297). The generated file
"py2/pkg2/bar.py" has following lines:

    import py2.pkg2.pkg3.pkg4.foo                          # [2]
    class Pkg2_Bar(py2.pkg2.pkg3.pkg4.foo.P1_S1_S2_Foo):  # [3]

and 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 4, in <module>
        from bar import Pkg2_Bar
      File "py2/pkg2/bar.py", line 71, in <module>
        class Pkg2_Bar(py2.pkg2.pkg3.pkg4.foo.Pkg4_Foo):
    AttributeError: 'module' object has no attribute 'pkg2'

It seems like during the import [1], the subpackage pkg2 is not yet fully
initialized, so py2.pkg2 can't be used. The above exception is raised at
line [3]. The problem disappears, for example, if we force swig to use relative
package names.

The difference between this ('from_init3') case and the case
'from_init2' is that here we import base class from module
pyX.pkg2.pkg3.pkg4.foo, which is nested deeper than it was in
'from_init2'. This is just to ensure, that two (and more) levels of
subpackages get imported correctly by generated python code, i.e, not only
'pkg3.foo' is handled properly (one-level subpackage) but the code works also
for 'pkg3.pkg4.foo', and so on.

If everything works well, the package pyX.pkg2 shall load properly.

Unix:
-----
- Run make
- Run the test as described above