python Get current workspace and then re-source to new SDE

Question

I am trying to write some code that will get the current workspace name and if it matches a particular datasource path, it will re-path the SDE layers to the new database. Initially I had the code working by just running the re-source code on ArcMap startup but this caused problems with the MXD's "Store relative pathnames" option in MXD and would turn it off. The problem I am having is that I am not sure how to tell it "if the workspace is "blah.sde" then only run the resource code. The MXD's connect to 3 SDE's. Here is what I have:

import arcpy
import pythonaddins
from arcpy import env

class ExtensionClass1(object):
"""Implementation for python_addin.extension2 (Extension)"""
def __init__(self):
    # For performance considerations, please remove all unused methods in 
this class.
    self.enabled = True
def startup(self):
    mxd = arcpy.mapping.MapDocument("CURRENT")
    if arcpy.env.workspace = r"C:\ArcGIS\blah.sde":
        mxd.findAndReplaceWorkspacePaths(r"C:\ArcGIS\blah.sde", 
                                     r"C:\ArcGIS_10.3.1\blah.sde")
        mxd.findAndReplaceWorkspacePaths(r"C:\ArcGIS\blah2.sde", 
                                     r"C:\ArcGIS_10.3.1\blah2.sde")
        mxd.findAndReplaceWorkspacePaths(r"C:\ArcGIS\blah3.sde", 
                                     r"C:\ArcGIS_10.3.1\blah3.sde")
        arcpy.RefreshActiveView()
        arcpy.RefreshTOC()


def openDocument(self):
    mxd = arcpy.mapping.MapDocument("CURRENT")
    if arcpy.env.workspace = r"C:\ArcGIS\blah.sde":
        mxd.findAndReplaceWorkspacePaths(r"C:\ArcGIS\blah.sde", 
                                     r"C:\ArcGIS_10.3.1\blah.sde")
        mxd.findAndReplaceWorkspacePaths(r"C:\ArcGIS\blah2.sde", 
                                     r"C:\ArcGIS_10.3.1\blah2.sde")
        mxd.findAndReplaceWorkspacePaths(r"C:\ArcGIS\blah3.sde", 
                                     r"C:\ArcGIS_10.3.1\blah3.sde")
        arcpy.RefreshActiveView()
        arcpy.RefreshTOC()

Answer 1

One option would be to check the layers source in the mxd and use the .find() method to check the returned string for any instance of ".sde":

for lyr in arcpy.mapping.ListLayers(mxd):
    found = lyr.dataSource.find('.sde')
    if found > -1:
        print 'sde layer found'
        # run resource code