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I had problem to import vmware module due to lack of it's dep. The
message in log though was saying that there is no vmware module, which
is far from true. The problematic code is at least:

/usr/lib/python2.6/site-packages/nova/openstack/common/importutils.py

def import_class(import_str):
...
    try:
        __import__(mod_str)
        return getattr(sys.modules[mod_str], class_str)
    except (ValueError, AttributeError):
        raise ImportError('Class %s cannot be found (%s)' %
                          (class_str,
                           traceback.format_exception(*sys.exc_info())))

Which would obfuscate the error message when some module import dies on
ValueError, and:


def import_object_ns(name_space, import_str, *args, **kwargs):
    """Tries to import object from default namespace.

    Imports a class and return an instance of it, first by trying
    to find the class in a default namespace, then failing back to
    a full path if not found in the default namespace.
    """
    import_value = "%s.%s" % (name_space, import_str)
    try:
        return import_class(import_value)(*args, **kwargs)
    except ImportError:
        return import_class(import_str)(*args, **kwargs)

Which will say ImportError: Missing module import_str, but only as a
result of failure of the first import in the try-except block,
effectively hiding the true reason of the failure.

In other words, if the first import fails for some interesting reasons,
some other, possible meaningles import is tried and only it's error is
let to propagate.


+++ This bug was initially created as a clone of Bug #1080424 +++

Description of problem:
When having nova-compute alone on a node, I cannot start it (using PYTHONVERBOSE=1 and slightly modified init script for debuging purposes):

2014-03-25 11:10:42.153 10009 INFO nova.virt.driver [-] Loading compute driver 'vmwareapi.VMwareVCDriver'
import nova.virt.vmwareapi # directory /usr/lib/python2.6/site-packages/nova/virt/vmwareapi
# /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/__init__.pyc matches /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/__init__.py
import nova.virt.vmwareapi # precompiled from /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/__init__.pyc
# /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/driver.pyc matches /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/driver.py
import nova.virt.vmwareapi.driver # precompiled from /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/driver.pyc
# /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/error_util.pyc matches /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/error_util.py
import nova.virt.vmwareapi.error_util # precompiled from /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/error_util.pyc
# /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/host.pyc matches /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/host.py
import nova.virt.vmwareapi.host # precompiled from /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/host.pyc
# /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vim_util.pyc matches /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vim_util.py
import nova.virt.vmwareapi.vim_util # precompiled from /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vim_util.pyc
# /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vm_util.pyc matches /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vm_util.py
import nova.virt.vmwareapi.vm_util # precompiled from /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vm_util.pyc
# /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vim.pyc matches /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vim.py
import nova.virt.vmwareapi.vim # precompiled from /usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vim.pyc
2014-03-25 11:10:42.155 10009 ERROR nova.virt.driver [-] Unable to load the virtualization driver
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver Traceback (most recent call last):
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver   File "/usr/lib/python2.6/site-packages/nova/virt/driver.py", line 1115, in load_compute_driver
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver     virtapi)
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver   File "/usr/lib/python2.6/site-packages/nova/openstack/common/importutils.py", line 54, in import_object_ns
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver     return import_class(import_str)(*args, **kwargs)
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver   File "/usr/lib/python2.6/site-packages/nova/openstack/common/importutils.py", line 30, in import_class
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver     __import__(mod_str)
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver ImportError: No module named vmwareapi
2014-03-25 11:10:42.155 10009 TRACE nova.virt.driver 


when trying to imprort it in ipython:
In [1]: import nova.virt.vmwareapi
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-1-c0f052a58780> in <module>()
----> 1 import nova.virt.vmwareapi

/usr/lib/python2.6/site-packages/nova/virt/vmwareapi/__init__.py in <module>()
     19 """
     20 # NOTE(sdague) for nicer compute_driver specification
---> 21 from nova.virt.vmwareapi import driver
     22 
     23 VMwareESXDriver = driver.VMwareESXDriver

/usr/lib/python2.6/site-packages/nova/virt/vmwareapi/driver.py in <module>()
     37 from nova.virt.vmwareapi import error_util
     38 from nova.virt.vmwareapi import host
---> 39 from nova.virt.vmwareapi import vim
     40 from nova.virt.vmwareapi import vim_util
     41 from nova.virt.vmwareapi import vm_util

/usr/lib/python2.6/site-packages/nova/virt/vmwareapi/vim.py in <module>()
     25 
     26 from oslo.config import cfg
---> 27 import suds
     28 
     29 from nova.openstack.common.gettextutils import _

ImportError: No module named suds



Version-Release number of selected component (if applicable):
openstack-nova-compute-2013.2.2-2.el6ost.noarch
python-nova-2013.2.2-2.el6ost.noarch

How reproducible:
always

Steps to Reproduce:
1. Install nova-compute
2. do the import in the python interpret


Actual results:
ImportError: No module named suds

Expected results:
no problem

Additional info:

** Affects: nova
     Importance: Undecided
         Status: New

-- 
messages when the module import fails are very misleading and not descriptive
https://bugs.launchpad.net/bugs/1297261
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