Question

I’m trying to integrate a project Project A built by a colleague into another python project. Now this colleague has not used relative imports in his code but instead done

from packageA.moduleA import ClassA
from packageA.moduleA import ClassB

and consequently pickled the classes with cPickle. For neatness I’d like to hide the package that his (Project A) built inside my project. This however changes the path of the classes defined in packageA. No problem, I’ll just redefine the import using

from ..packageA.moduleA import ClassA
from ..packageA.moduleA import ClassB

but now the un pickling the classes fails with the following message

    with open(fname) as infile: self.clzA = cPickle.load(infile)
ImportError: No module named packageA.moduleA

So why doesn’t cPickle apparently see the module defs. Do I need to add the root of packageA to system path? Is this the correct way to solve the problem?

The cPickled file looks something like

ccopy_reg
_reconstructor
p1
(cpackageA.moduleA
ClassA
p2
c__builtin__
object
p3
NtRp4

The old project hierarchy is of the sort

packageA/
    __init__.py
    moduleA.py
    moduleB.py
packageB/
    __init__.py
    moduleC.py
    moduleD.py

I’d like to put all of that into a WrapperPackage

MyPackage/
.. __init__.py
.. myModuleX.py
.. myModuleY.py
WrapperPackage/
.. __init__.py
.. packageA/
   .. __init__.py
   .. moduleA.py
   .. moduleB.py
.. packageB/
   .. __init__.py
   .. moduleC.py
   .. moduleD.py

Answer 1

You’ll need to create an alias for the pickle import to work; the following to the __init__.py file of the WrapperPackage package:

from .packageA import * # Ensures that all the modules have been loaded in their new locations *first*.
from . import packageA  # imports WrapperPackage/packageA
import sys
sys.modules['packageA'] = packageA  # creates a packageA entry in sys.modules

It may be that you’ll need to create additional entries though:

sys.modules['packageA.moduleA'] = moduleA
# etc.

Now cPickle will find packageA.moduleA and packageA.moduleB again at their old locations.

You may want to re-write the pickle file afterwards, the new module location will be used at that time. The additional aliases created above should ensure that the modules in question have the new location name for cPickle to pick up when writing the classes again.