请问如何从一长字符串中，随机截取n段相同长度的短字符串？

如从‘abcdefghijklmnopqrstuvwxyz’中随机产生['ab',''ef','ij','op']，多个2bp不重复的字符串。

import random

str1 ='abcdefghijklmnopqrstuvwxyz'
lst = random.sample(str1[:-2], 5)
lst1 = []
for one in lst:
    #print(str1.index(one))
    lst1.append(one + str1[str1.index(one)+1])
print(lst1)

import random
s = "abcdefghijklmnopqrstuvwxyz"
a = []
time = eval(input())
for i in range(time*2):
    d = ""
    while True:
        c = random.choice(s)
        if c not in a:
            d += str(c)
            break
    a.append(d)
e = []
for i in range(time):
    e.append("{}{}".format(a[i*2],a[i*2+1]))
print(e)