My walk code will not skip reading the worksheets inside excel files. Staff have excel files with a huge amount of worksheets that is slowing my walk down so that it is basically unusable. I think it is still reading the excel worksheets in the else statement.
import arcpy, os, traceback, sys
arcpy.env.overwriteOutput = True
workspace = r"C:\Users\Documents\GisData"
arcpy.env.workspace = workspace
try:
    walk = arcpy.da.Walk(workspace)
    txt = open(r"C:\Users\Documents\StaffGISLibrary.txt", 'w')
    for dirpath, dirnames, filenames in walk:
        if arcpy.Exists(dirpath):
            #describe = arcpy.Describe(dirpath)
            if dirpath.endswith(('.xls', '.xlsx', '.txt')):
                print "skipping excel file"
                pass
            else:
                for filename in filenames:
                    fullpath = os.path.join(dirpath, filename)
                    describe = arcpy.Describe(fullpath)
                    print "writing " + fullpath
                    txt.write(fullpath + "," + filename + "," + describe.dataType + "\n")
        else:
            print "DOES NOT EXIST"
            pass
    del filename, dirpath, dirnames, filenames
    txt.close() 
except Exception, e:
    pass
    # If an error occurred, print line number and error message
    import traceback, sys
    tb = sys.exc_info()[2]
    print "Line %i" % tb.tb_lineno
    print e.message
finally:
    raw_input("Finished!")