A little language for schema-enforced models

Fame is a framework for metamodelling in Python.

• Entities are described by models

• Models are described by metamodels

• Models have fields, derived fields and constraints

• Entities can have custom fields

• Entities can be created even if data is invalid

• There are functions to validate and get error messages

• Validation checks presence and type of fields

• Validation checks all constraints

• Derived fields are memoized

Example

class Experiment(Model):

    @schema
    def metamodel(self, m):
        m.field('name', str)
        m.field('subject', options(
            'user',
            'visitor',
            'email',
            'listing',
            'market'
        ))
        m.field('treatments', array(str))
        m.field('percent_exposed', int, default=100)
        m.field('design', nullable(regexp('^https?')))

    @derived_field
    def is_miscellanous(self):
        return self.subject not in ['user', 'visitor']

    @constraint("expected percent_exposed to not exceed 100, got {}")
    def constraint(self):
        if self.percent_exposed > 100:
            return self.percent_exposed

Conventions

• Define metamodel function first

• Then define derived field functions

• Then define all the constraint functions

• Constraint functions are all named “constraint”, that is intentional

pip install fame