I have a file with few thousand lines like this:

```
0.5  AA
2.7 AA
45.2 AA
567.1 CC
667.5 AA 
4456 AA
1005.2 CC

```

I want add comment signs "//" at the beginning of each line contains string "CC".

I have code like this:

```
import fileinput

file_name = input("file path: ")

for line in fileinput.FileInput(file_name, inplace=1):
    if 'CC' in line:
        line = line.rstrip()
        line = line.replace(line,'// '+line)
    print (line)

```

Everything works fine but the file looks like that after execute the code:

```
0.5  AA

2.7 AA

45.2 AA

// 567.1 CC
667.5 AA

4456 AA

// 1005.2 CC

```

Why after execute the code i have the new line spaces after line without changes? How I can remove this?
Second question is: How i can save this file as a new file?

Summarizing:
I need to write code which in a txt file will add "//" to the beginning of each line containing "CC" and save it as a new file.