Open Eclipse.

From the Window menu, select Preferences.

In the pane on the left-hand side of the Preferences window, click on the arrow icon next to PyDev.

From the list of PyDev preferences, select Interpreters.

In the pane labeled Python Interpreters, click on the New button.

In the Select interpreter dialog, name the interpreter PyQGIS.

Navigate to the location of the Python interpreter called python.exe, placed within the bin folder of the QGIS program folder. On OS X and Linux, you use the system's Python installation. On Windows, Python is included with QGIS. The default location on Windows is C:\Program Files\QGIS2.18\bin\python.exe, as shown in the following screenshot:

When you click on the OK button, Eclipse will attempt to automatically add every Python library it finds to the Python path to configure this interpreter. We need to control which libraries are added to prevent conflicts. Click on the Deselect All button and then click on OK:

Eclipse will issue a warning dialog because you haven't selected any core libraries. Click on the Proceed anyways button, as shown here:

Start QGIS.

Select Python Console from the Plugins menu.

Use the sys module to locate the PyQGIS Python path, as described in the previous recipe, Setting the environment variables:

        import sys 
        sys.path 

We also want to add the PyQGIS API so the script has access to all of the QGIS functions within Eclipse. Next, find that path using the QGIS Python Console by typing the following command:

      qgis

For each path in the returned list, click on the New Folder button in Eclipse's Libraries pane for your QGIS interpreter and browse to that folder until all the paths have been added. If a given folder does not exist on your system, simply ignore it, as shown here:

Click on the OK button in the Preferences dialog.

In the PyDev preferences for the PyQGIS interpreter, select the Forced Builtins tab, as shown in the following screenshot:

Click on the New button.

In the Builtin to add dialog, type qgis:

Click on the OK button.

In the PyDev preferences dialog, ensure that the PyQGIS interpreter is selected from the list of interpreters.

Select the Environment tab.

Click on the New button.

In the Name field, enter PATH.

For the Value field, add the path to the QGIS program directory and to any QGIS directories that contain binaries separated by a semicolon. The following is an example from a Windows machine:

  C:\Program Files\QGIS 2.18;C:\Program Files\QGIS 2.18\bin;
      C:\Program Files\QGIS 2.18\apps\qgis\bin;C:\Program Files\QGIS
      2.18\apps\Python27\DLLs