pyqgis - Understanding qgis.core import error: no module named qgis.core?

I searched all the same questions, and none of them works for me, so i decided to ask this question in addition to those:

I installed QGIS 2.18 via this downloaded setup 'QGIS-OSGeo4W-2.18.11-1-Setup-x86_64.exe'.

and my PATH system variables are :

C:\Program Files (x86)\AMD APP\bin\x86_64;C:\Program Files (x86)\AMD APP\bin\x86;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\ATI Technologies\ATI.ACE\Core-Static;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;%PYTHONHOME%;%PYTHONHOME%\Scripts;C:\Program Files\QGIS 2.18\bin;%PATH%

my PATH user variables:

C:\Users\ash\AppData\Local\Programs\Python\Python36-32\Scripts\;C:\Users\ash\AppData\Local\Programs\Python\Python36-32\

PYTHONHOME :

C:\Program Files\QGIS 2.18\apps\Python27

PYTHONPATH :

C:\Program Files\QGIS 2.18\apps\Python27\Lib

*** I use pycharm and my project interpreter is :

Python 2.7.5 (C:\Program Files\QGIS 2.18\bin\python.exe

now if I import qgis.core it will give

import error: no module named qgis.core

error in pycharm, but no errors in qgis python console!!!

What did I do wrong?

Answer

I found it, it was just a small tricky approach.

in OsGeo4w website says you have to install QGIS by Osgeo4w setup which it sets all kinds of path variables for you ...

( it was NOT entirely true, in my case)

leave your PATH, Path, PYTHONPATH, PYTHONHOME to where it's functional for all modules unless qgis's.

I removed QGIS standalone and installed QGIS via OsGeo4w however. so the path variables that I wrote in the question must change to the same directories but NOT in QGIS 2.18 ROOT, rather in C:\OSGeo4W64.

for example, my PYTHONHOME is now :

C:\OSGeo4W64\apps\Python27

and so on...

so I created a whatever.cmd file using notepad, with this information in it :

@echo off

SET OSGEO4W_ROOT=C:\OSGeo4W64

call "%OSGEO4W_ROOT%"\bin\o4w_env.bat

call "%OSGEO4W_ROOT%"\apps\grass\grass-6.4.3\etc\env.bat

@echo off

path %PATH%;%OSGEO4W_ROOT%\apps\qgis\bin

path %PATH%;%OSGEO4W_ROOT%\apps\grass\grass-6.4.3\lib

set PYTHONPATH=%PYTHONPATH%;%OSGEO4W_ROOT%\apps\qgis\python;

set PYTHONPATH=%PYTHONPATH%;%OSGEO4W_ROOT%\apps\Python27\Lib\site-packages

set QGIS_PREFIX_PATH=%OSGEO4W_ROOT%\apps\qgis

set PATH=C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.4\bin;%PATH%

start "PyCharm aware of Quantum GIS" /B "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.4\bin\pycharm64.exe" %*

and saved it to somewhere.

So if you use Qgis standalone just instead of osgeo_root write your qgis_root directory.

the few last line are dedicated to familiarizing all this mess to Pycharm.

be careful of typing mistakes. I learned, one wrong char can mess it up...