maya_modeleditor.py

import pymel.core.uitypes as pmui

model_panel = pmui.ModelEditor(pm.getPanel(withFocus=True))
print pmui.ModelEditor.getRendererName(model_panel)

# Although, that snippet seems to be temperamental. It sometimes throws an error complaining that the model editor was not found, especially when executed from the shelf.

# Another way would be a bit wordy, but it works everytime:

import pymel.core as pm
import pymel.core.uitypes as pmui

modelPanelList = []
modelEditorList = pm.lsUI(editors=True)
for myModelPanel in modelEditorList:
    if myModelPanel.find('modelPanel') != -1:
        modelPanelList.append(myModelPanel)

for modelPanel in modelPanelList:    
    if pmui.ModelEditor(modelPanel).getActiveView():
        try:
            # Always better to try in the case of active panel operations
            # as the active panel might not be a viewport.
            print pmui.ModelEditor(modelPanel).getRendererName()
        except Exception as e:
            # Handle exception
            print e

# A concise, pseudo-PyMEL way would be to just PyMEL-ify Tomek's answer:

import pymel.core as pm
print pm.modelEditor(pm.getPanel(wf=True), q=True, rnm=True)

To get a list of viewport renderers:

import pymel.core.uitypes as pmui
print pmui.ModelEditor().getRendererList()

# Here is some extra info on model editors and viewport renderers. To get their "friendly" names:

import pymel.core.uitypes as pmui
print pmui.ModelEditor().getRendererListUI()

# To set them, concisely, I would use PyMEL and do:

import pymel.core.uitypes as pmui

# assuming you know which modelPanel you want to affect
pmui.ModelEditor("modelPanel4").setRendererName("ogsRenderer")

# To affect all viewports (modelPanels) I would do:

import pymel.core as pm
import pymel.core.uitypes as pmui

modelPanelList = []
modelEditorList = pm.lsUI(editors=True)
for myModelPanel in modelEditorList:
    if myModelPanel.find('modelPanel') != -1:
        modelPanelList.append(myModelPanel)

for modelPanel in modelPanelList:
    pmui.ModelEditor(modelPanel).setRendererName("ogsRenderer")

# To affect just the viewport in focus:

import pymel.core as pm
import pymel.core.uitypes as pmui

modelPanelList = []
modelEditorList = pm.lsUI(editors=True)
for myModelPanel in modelEditorList:
    if myModelPanel.find('modelPanel') != -1:
        modelPanelList.append(myModelPanel)

for modelPanel in modelPanelList:    
    if pmui.ModelEditor(modelPanel).getActiveView():
        try:
            # Always better to try in the case of active panel operations
            # as the active panel might not be a viewport.
            pmui.ModelEditor(modelPanel).setRendererName("ogsRenderer")
        except Exception as e:
            # Handle exception
            print e