Deprecation warning due to invalid escape sequences

Deprecation warnings are raised due to invalid escape sequences. This can be fixed by using raw strings or escaping the literals. pyupgrade also helps in automatic conversion : https://github.com/asottile/pyupgrade/

```
find . -iname '*.py' | xargs -P4 -I{} python3.8 -Wall -m py_compile {}
./tests/test_layouts.py:23: DeprecationWarning: invalid escape sequence \ 
  '''
```