替换文件的头部与另一个文件

Question

的内容我有两个文件：

文件：

line A_1 
line A_2 
line A_3 
... 
line A_n 

文件B：

line B_1 
line B_2 
... 
line B_n 
line B_n+1 
... 
line B_m 

我想第一n线文件A替换文件B的第一行n行（m > n）。此文件后乙方应是这样的：

文件B：

line A_1 
... 
line A_n 
line B_n+1 
... 
line B_m 

什么是最Python的解决方案呢？

Answer 1

with open("newB.txt","wb") as fout: 
    with open("B.txt") as b: 
     for lineA,lineB in zip(open("A.txt"),b): 
      fout.write(lineA) 
     fout.writelines(b) 

也许......我想......

Answer 2

with open(A) as fp_A: 
    for i, line in enumerate(fp_A): 
     if i <= n: 
      print(line) 
     else: 
      break 
with open(B) as fp_B: 
    for i, line in enumerate(fp_B): 
     if i > n: 
      print(line)