Something

import maya.cmds as mc
 
forestsGlobalItem = None
 
def User_Select():
    global forestsGlobalItem

    print "USER"
    ctx=mc.scriptCtx( title='Select Something', totalSelectionSets=1,\
        fcs="select -r $Selection1; python(\"Sel_Func('\"+$Selection1[0]+\"')\");",\
        cumulativeLists=False, expandSelectionList=True, setNoSelectionPrompt='Select Object',\
        setSelectionPrompt='Never used', setDoneSelectionPrompt='Never used because setAutoComplete is set',\
        setAutoToggleSelection=True, setSelectionCount=1, setAutoComplete=True)

    mc.setToolTo(ctx)
    forestsGlobalItem = None
    while forestsGlobalItem is None:
        pass
    item = forestsGlobalItem
    forestsGlobalItem = None
    return item

def Sel_Func(item):
    global forestsGlobalItem

    print "PRINT My Function", item
    forestsGlobalItem = item