I have the following function. The program looks at each file and prints the lines occuring in all 4 files to a new file. I've tried `file1.close()` but I get an error about closing a set? I think I could use a `with` statement but not sure how to do this, I'm very new to programming.

```
def secretome():
    file1 = set(line.strip() for line in open(path + "goodlistSigP.txt"))
    file2 = set(line.strip() for line in open(path + "tmhmmGoodlist.txt"))
    file3 = set(line.strip() for line in open(path + "targetpGoodlist.txt"))
    file4 = set(line.strip() for line in open(path + "wolfPsortGoodlist.txt"))
    newfile = open(path + "secretome_pass.txt", "w")
    for line in file1 & file2 & file3 & file4:
        if line:
            newfile.write(line + '\n')
    newfile.close()

```