When I try to load qgis within an external Python instance, I get the following error: 

```
>>> from PyQt4.QtCore import *
>>> from PyQt4.QtGui import *
>>> import qgis
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "E:\QGIS\apps\qgis\python\qgis\__init__.py", line 27, in <module>
    from qgis.core import QgsFeature, QgsGeometry
  File "E:\QGIS\apps\qgis\python\qgis\core\__init__.py", line 30, in <module>
    from qgis._core import *
ImportError: DLL load failed: The specified procedure could not be found.

```

QGIS version: 2.16.1. 

Python in QGIS: 

```
>>> print(sys.version)
2.7.5 (default, May 15 2013, 22:44:16) [MSC v.1500 64 bit (AMD64)]

```

Python installation: 

```
>>> print(sys.version)
2.7.12 (v2.7.12:d33e0cf91556, Jun 27 2016, 15:24:40) [MSC v.1500 64 bit (AMD64)]

```

Paths in Python installation: 

```
>>> print(sys.path)
['', 'E:\\QGIS\\apps\\qgis\\python', ... 

```

Additionally the following paths are set in the environment of Windows: 

```
E:\QGIS\apps\qgis\python;E:\QGIS\apps\qgis\bin;

```

Any idea how to fix this? Or how shall I setup my system to be able to access QGIS "interactively" from external Python IDEs ?