Examples/python/import_packages/from_init1/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/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