写入文本文件每一行中的两个特定位置（或者创建一个添加了信息的新文件）

Question

aspiring Python newb (2 months) here. I am trying to create a program that inserts information to two specific places of each line of a .txt file, actually creating a new file in the process.

The information in the source file is something like this:

1,340.959,859.210,0.0010,VV53
18abc,34099.9590,85989.2100,0.0010,VV53
00y46646464,34.10,859487.2970,11.4210,RP27

Output would be:

1,7340.959,65859.210,0.0010,VV53
18abc,734099.9590,6585989.2100,0.0010,VV53
00y46646464,734.10,65859487.2970,11.4210,RP27

Each line different, hundreds of lines. The specific markers I'm looking for are the first and second occurence of a comma (,). The stuff needs to be added after the first and second comma. You'll know what I mean when you see the code.

I have gotten as far as this: the program finds the correct places and inserts what I need, but doesn't write more than 1 line to the new file. I tried debugging and seeing what's going on 'under the hood', all seemed good there.

Lots of scrapping code and chin-holding later I'm still stuck where I was a week ago.

tl;dr Code only outputs 1 line to new file, need hundreds.

f = open('test.txt', 'r')
new = open('new.txt', 'w')

first = ['7']
second = ['65']
line = f.readline()
templist = list(line)
counter = 0

while line != '':
    for i, j in enumerate(templist):
        if j == ',':
            place = i + 1
            templist1 = templist[:place]
            templist2 = templist[place:]
            counter += 1    
            if counter == 1:
                for i, j in enumerate(templist2):
                    if j == ',':
                        place = i + 1
                        templist3 = templist2[:place]
                        templist4 = templist2[place:]
                        templist5 = templist1 + first + templist3 + second + templist4
                        templist6 = ''.join(templist5)
                        new.write(templist6)
                        counter += 1
                        break                     
                if counter == 2:
                    break
            break

    line = f.readline()
    templist = list(line)

f.close()
new.close()

Answer 1

If I'm understanding your samples and code correctly, this might be a valid approach:

with open('test.txt', 'r') as infd, open('new.txt', 'w') as outfd:
    for line in infd:
        fields = line.split(',')
        fields[1] = '7' + fields[1]
        fields[2] = '65' + fields[2]
        outfd.write('{}\n'.format(','.join(fields)))