Launching Processing tool User Interface using PyQGIS

I am trying to launch the UI of a processing algorithm using Python script but I cannot find a simple way for it (aside double clicking on it in the process toolbox of course). The plugin is a water network simulator and I just want to launch its pre-processing UI without using process.runalg() because this needs to enter arguments and I don't need it.

Some ways would be to trigger processes available in process toolbox or sending command to commander from python console. but I have no clue how and I am searching for 2 hours now, no results.

Answer

You can do that from the QGIS Python console in this way:

# Import both Processing and CommanderWindow 
#   classes from the Processing framework. 

from processing.core.Processing import Processing
from processing.gui.CommanderWindow import CommanderWindow

# Then get the algorithm you're interested in (for instance, Join Attributes):
alg = Processing.getAlgorithm("qgis:joinattributestable")

# Instantiate the commander window and open the algorithm's interface 
cw = CommanderWindow(iface.mainWindow(), iface.mapCanvas())
if alg is not None:
    cw.runAlgorithm(alg)

That's it! You get the algorithm's UI open.

Note: You can get the names of the available algorithms by entering these lines in the QGIS Python console:

import processing
processing.alglist()

Tested in QGIS 2.10.1, Processing framework v.2.9.1 and v.2.10.1

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EDIT:

If you find errors when running the code snippet above, chances are you're using QGIS v2.16.0, v2.16.1, or v2.16.2. To solve the issue, install QGIS v2.16.3.