替换文件中的整行

Question

我有一个.txt文件，里面的数据是这样的：

0,Rent1,Expense,16/02/2010,1,4000,4000  
0,Car Loan1,Expense,16/02/2010,2,4500,9000  
0,Flat Loan1,Expense,16/02/2010,2,4000,8000  
0,Rent2,Expense,16/02/2010,1,4000,4000  
0,Car Loan2,Expense,16/02/2010,2,4500,9000  
0,Flat Loan2,Expense,16/02/2010,2,4000,8000 

现在我想把第4行替换成新的内容，比如：

0,Loan,Expense,19/02/2010,2,5000,10000

我使用了以下代码：

newline='0,Loan,Expense,19/02/2010,2,5000,10000'
lnum=1
for line in fileinput.FileInput("sample.txt",inplace=1):
    if lnum=='4':
        result = newline
        lnum=lnum+1
    else:
        result=line
        lnum=lnum+1
    sys.stdout.write(result)

但是文件里显示的是：

0,Rent1,Expense,16/02/2010,1,4000,4000  
0,Car Loan1,Expense,16/02/2010,2,4500,9000  
0,Flat Loan1,Expense,16/02/2010,2,4000,8000  
0,Loan,Expense,19/02/2010,2,5000,100000,Car Loan2,Expense,16/02/2010,2,4500,9000
0,Flat Loan2,Expense,16/02/2010,2,4000,8000 

我该怎么解决这个问题呢？

Answer 1

使用enumerate：代码更少，出错的可能性也更小

newline = '0,Loan,Expense,19/02/2010,2,5000,10000\n'
for lnum, line in enumerate(fileinput.FileInput("sample.txt",inplace=1)):
    if lnum == 4:
        line = newline
sys.stdout.write(line)

Answer 2

添加一个新行

newline='0,Loan,Expense,19/02/2010,2,5000,10000'
lnum=1
for line in fileinput.FileInput("sample.txt",inplace=1):
    if lnum==4:
        result = newline+"\n"
    else:
        result=line
    lnum=lnum+1    
    sys.stdout.write(result)

或者你可以直接声明一个 newline 变量，像这样

newline="0,Loan,Expense,19/02/2010,2,5000,10000\n"

Answer 3

把下面的内容替换掉：

result = newline #you lose the newline here

换成：

result = newline + '\n' #or '\r\n' depending on your newline format.