I'm trying to write a simple Python script which takes a text file as an input, deletes every non-literal character, and writes the output in another file.
Normally I would have done two ways:

* use a regular expression combined with `re.sub` to replace every non letter character with empty strings
* examine every char in every line and write it to the output only if it was in `string.lowercase`

But this time the text is The Divine Comedy in Italian (I'm Italian), so there are some Unicode characters like

```
èéï

```

and some others. I wrote `# -*- coding: utf-8 -*-` as the first line of the script, but what I got is that Python doesn't signal errors when Unicode chars are written inside the script.

Then I tried to include Unicode chars in my regular expression, writing them as, for example:

```
u'\u00AB'

```

and it seems to work, but Python, when reading input from a file, doesn't rewrite what it read the same way it read it. For example, some characters get converted into square root symbol.

What should I do?