Reformat seq_module.py

Check out the docs for [Python format strings](https://docs.python.org/2/library/string.html#formatstrings):

> The _conversion_ field causes a type coercion before formatting. Normally, the job of
> formatting a value is done by the `__format__()` method of the value itself. However,
> in some cases it is desirable to force a type to be formatted as a string, overriding its
> own definition of formatting. By converting the value to a string before calling
> `__format__()`, the normal formatting logic is bypassed.
> 
> Two conversion flags are currently supported: `'!s'` which calls `str()` on the value,
> and `'!r'` which calls `repr()`.