States required

attribute-required.py

class Contract:                                                                                                                             
    """                                                                                                                                     
    This overwrite of class Contract extend functionality of Contract                                                                       
    vanilla model.                                                                                                                          
    Add the necessary functions to represent a ISP Contract.                                                                                
    """                                                                                                                                     
    __metaclass__ = PoolMeta                                                                                                                
    __name__ = 'contract'                                        
    equipment_received = fields.Boolean('Equipment Received', states={
        'required': Eval('state') in ['activation_scheduled', 'introduced']
        })

Debes utilizar el operador in de PYSON y no el estandard de python