I need to be able to reverse a whole file, or at least the contents of it. My code so far is:

```
def reverse_file(of, rf):
     oldfile = open(of, 'r')
     reversefile = open(rf, 'w')
     filedata = oldfile.read()
     rdata = str_reverse(filedata)
     reversefile.write(rdata)
     oldfile.close()
     reversefile.close()

```

The problem is I need to define `str_reverse` and I'm not sure how to create a function that reverses everything. Any help?