I'm just trying to understand the "keys =" line of code in the following script. This script was pulled in an answer linked below. I would just comment on that section but I don't have enough points to comment. 

[Search Multiple Strings (from File) in a file and print the line](https://stackoverflow.com/questions/37902523/search-multiple-strings-from-file-in-a-file-and-print-the-line)

I am having a hard time finding documentation on what "key for key" is. From what I found, it is part of the dictionary but any help in understanding that part would be greatly appreciated. Thanks!

```
keyfile = "keys.txt"
testfile = "test.txt"

keys = [key for key in (line.strip() for line in open(keyfile)) if key]

with open(testfile) as f:
for line in f:
    for key in keys:
        if key in line:
            print(line, end='')
            break

```