Impacted versions:10

Steps to reproduce:
Following the code in https://www.odoo.com/documentation/10.0/api_integration.html both in a fresh install and against 'https://demo.odoo.com/start' trows a type error

Current behavior:
Now I get an error when executing:

```
ids = models.execute_kw(db, uid, password,  'res.partner', 'search',
    [[['is_company', '=', True], ['customer', '=', True]]],
    {'limit': 1})
[record] = models.execute_kw(db, uid, password,
    'res.partner', 'read', [ids])
# count the number of fields fetched by default
len(record)
```

In particular it seems to be a type error (cannot marshal class odoo.tools.float_utils.float_precision)

Expected behavior:
I would expect it to behave as in the documentation

""" Basic string field, can be length-limited, usually displayed as a
    single-line string in clients.
    :param int size: the maximum size of values stored for that field
    :param translate: enable the translation of the field's values; use
        ``translate=True`` to translate field values as a whole; ``translate``
        may also be a callable such that ``translate(callback, value)``
        translates ``value`` by using ``callback(term)`` to retrieve the
        translation of terms.
    """
    type = 'char'
    _slots = {
        'size': None,                   
    }
    _column_size = property(attrgetter('size'))
    _related_size = property(attrgetter('size'))
    _description_size = property(attrgetter('size'))
    def _setup_regular_base(self, model):
        super(Char, self)._setup_regular_base(model)
        assert isinstance(self.size, (NoneType, int)), \
            "Char field %s with non-integer size %r" % (self, self.size)
    def convert_to_cache(self, value, record, validate=True):
        if value is None or value is False:
            return False
        return ustr(value)[:self.size]
class Text(_String):