sp1 = f1.readlines()
sp2 = range(n)
for i in range(n):
    sp2[i] = range(3)    
    
for i in range(n):
    sp2 = sp1[i].split()
    for j in range(3):
        sp1[i][j] = sp2[j]#ошибка 'str' object does not support item assignment
        
for i in range(n): #вывод массива на экран
    for j in range(3):
        print sp1[i][j],
    print

sp = []
for stroka in f1.readlines():
    sp.append(stroka.split())
print sp

for line in f.readlines():
   if len(line.split())!=3: 
      sp.append(line.split().append(""))
   else:
      sp.append(line.split())
print sp

sp = []
k = []
for stroka in f1.readlines():
    if(len(stroka.split())!=3):
    	k = stroka.split()
    	k.append("")
    	sp.append(k)
    else:
    	sp.append(stroka.split())
print sp

sp = []
for stroka in f1.readlines():
    sp.append(stroka.split())
    while 3 > len(sp[-1]): # на случай, если попадется строка с одним словом :)
        sp[-1].append("")
print sp

sp = []
for stroka in f1.readlines():
    lst = stroka.split()
    sp.append(lst + ['']*(3-len(lst) ) )
print sp

print [item + ['']*(3-len(item)) for item in (stroka.split() for stroka in f1.readlines()) ]

for stroka in f1.readlines()

for stroka in f1

print [ item + ['']*(3-len(item)) for item in (line.split() for line in f1) ]