In python (and many languages) appending to a string actually creates a new entry into memory as strings are immutable. In this specific scenario you can just use a join.

``` py
def format_logs(logs):
    """Place newline characters at the end of each line"""
    return '\n'.join(logs)
```

I see that you're casting to a string. I'm not sure if that's necessary but if it is you can do this....

``` py
def format_logs(logs):
    """Place newline characters at the end of each line"""
    return '\n'.join(map(str, logs))
```