Create Definition Query from values in Excel

I received a shapefile containing 50 000 records which had been converted from a CAD master plan. The Layer field contained 102 unique values, but for my purposes I only needed to look at 52 of those values (and then start cleaning the data). The engineer gave me an excel document with the values I needed, so I wrote this script to set a definition query on the layer:

xls = r"C:\Documents\MyExcel.xlsxSheet1$"
mxd = arcpy.mapping.MapDocument("CURRENT")
lyr = arcpy.mapping.ListLayers(mxd,"my_layer")[0]
lst_qry = []

with arcpy.da.SearchCursor(xls,("Layer")) as cursor:
    for row in cursor:
        #build up the query for each unique value
        defn_qry = """ "Layer" = '{}' """.format(row[0])
        lst_qry.append(defn_qry)

#create a string from the values in the list by
#concatentating with OR and set as definition query
lyr.definitionQuery = ' OR '.join(lst_qry)

Even though I detest using it, I ran this in the Python Window in ArcMap as it’s really the quickest way to work some Python magic on layers in the current document.