Python - Ayuda con codigo, error Set changed size during iteration

gramatica={'noTerminales':"Z,E,A",'terminales':"a,b",'simboloInicial':"Z",'producciones':["Z=>E","E=>(E+T)","E=>(E+T)","E=>id","T=>alksdla"]}

c={"Z=>.E"}

cc={}

senial=True

while senial==True:

    cc=c

    for x in c:

        noterminal=x[4]

        if noterminal in gramatica['noTerminales']:

            for y in gramatica['producciones']:

                if (y[0]==noterminal):

                    y=y[:3]+"."+y[3:]

                    cc.add(y)

    if c!=cc:

        c=(c|cc)

    else:

        senial=False

for t in c:

    print(t)

cc=c.copy()