DecimalField ignores precision
You need to set the arguments using keywords max_digits and decimal_places:

```
class Foo(Model):
    foo_field = DecimalField(decimal_places=2)
```

```
+-------+---------------+------+-----+---------+----------------+
| Field | Type          | Null | Key | Default | Extra          |
+-------+---------------+------+-----+---------+----------------+
| id    | int(11)       | NO   | PRI | NULL    | auto_increment |
| df    | decimal(10,2) | NO   |     | NULL    |                |
+-------+---------------+------+-----+---------+----------------+
```
 Apologies, I feel pretty silly for not paying attention to the documentation.

Please do note that the docs says the decimal_places argument is simply _places_ at http://charlesleifer.com/docs/peewee/peewee/fields.html#field-types-table

At least under MySQL, DecimalField ignores the precision parameters passed to the constructor, and the created table always carries the decimal field with precision 10,5. 

Example code:

``` python
class Foo(peewee.Model):
    foo_field = DecimalField(15,2)

Foo.create_table()
```

Produces a table with foo_field type set to decimal(10,5)
