>>> from schema_factory import BaseSchema, FloatNode, StringNode, SchemaNode, IntegerNode
>>>
>>> class PointSchema(BaseSchema):
...     lat=FloatNode()
...     lng=FloatNode()
...
>>> class RegionSchema(BaseSchema):
...     name=StringNode()
...     population=IntegerNode(default=50)
...     country_code=StringNode(required=True, validators=[lambda x: len(x) == 2])
...     location=SchemaNode(PointSchema, default=None)
...     keywords=StringNode(array=True, default=[])
...
>>> region = RegionSchema(
...     name='Athens',
...     population='1234',
...     country_code='gr',
...     location={'lat': 32.7647, 'lng': 27.03}
... )
>>> print(region)
<RegionSchema instance, attributes:['country_code', 'keywords', 'location', 'name', 'population']>
>>> region_2 = RegionSchema(name='Athens')
Traceback (most recent call last):
    ...
schema.SchemaError: Missing Required Attributes: {'country_code'}
>>> region_3 = RegionSchema(
...     name='Athens',
...     country_code='gr',
...     location={'lat': 32.7647, 'lng': 27.03},
...     foo='bar'
... )
...
Traceback (most recent call last):
    ...
schema.SchemaError: Invalid Attributes RegionSchema for {'foo'}.