Strike_A_Match Python algorithm

def Splitdigrams (a="hello world"):
    b=a.upper().split()
    c=[]
    for i in b:
        if len(i)<=2:
            c.append(i)
        else:
            c.extend([i[x:x+2] for x in range(len(i)-1)])
    return c

def strike_a_match(str1=u"ΓΕΡΩΝ ΠΑΙΣΙΟΣ", str2=u"ΓΕΡΩΝ ΠΑΣΤΙΤΣΙΟΣ"):
    digrams1=Splitdigrams(str1)
    digrams2=Splitdigrams(str2)
    commondigrams=[]
    coef1=len(digrams1)
    coef2=len(digrams2)
    for i in digrams1:
        if i in digrams2:
            commondigrams.append(i)
            digrams2.remove(i)
    return (2.0*len(commondigrams)/(coef1+coef2))

print (strike_a_match())