Utilities and Helpers

class Role(Set):
    """
    Field filtering system using set-based operations.
    
    A Role defines which fields should be included or excluded from
    operations like export, serialization, or validation based on
    user permissions or context.
    """
    
    def __init__(self, function, fields):
        """
        Initialize role with filtering function and field set.
        
        Args:
            function (callable): Filter function taking field name, returns bool
            fields (iterable): Collection of field names this role affects
        """
    
    def __contains__(self, field_name):
        """
        Check if field is included in this role.
        
        Args:
            field_name (str): Field name to check
            
        Returns:
            bool: True if field should be included
        """

def import_string(import_name):
    """
    Import a class or function from a string path.
    
    Args:
        import_name (str): Dotted import path (e.g., 'mymodule.MyClass')
        
    Returns:
        object: Imported class or function
        
    Raises:
        ImportStringError: If import fails
    """

class ImportStringError(Exception):
    """
    Exception raised when import_string fails to import from string path.
    """

def listify(value):
    """
    Convert value to list format for consistent processing.
    
    Args:
        value: Value to convert (single item, list, tuple, etc.)
        
    Returns:
        list: Value as list
    """

def get_all_subclasses(cls):
    """
    Get all subclasses of a class recursively.
    
    Args:
        cls (type): Class to find subclasses of
        
    Returns:
        set: All subclasses including nested subclasses
    """

def get_ident():
    """
    Get current thread identifier for thread-safe operations.
    
    Returns:
        int: Thread identifier
    """

def setdefault(obj, attr, value, search_mro=False, overwrite_none=False):
    """
    Enhanced setdefault with MRO search and None overwrite options.
    
    Args:
        obj: Object to set attribute on
        attr (str): Attribute name
        value: Default value to set
        search_mro (bool): Whether to search method resolution order
        overwrite_none (bool): Whether to overwrite None values
        
    Returns:
        Current or newly set attribute value
    """

class Constant(int):
    """
    Special integer constant with string representation.
    
    Used for export levels and other enumerated constants that need
    both numeric and readable string representations.
    """
    
    def __new__(cls, value, name=None):
        """
        Create constant with value and optional name.
        
        Args:
            value (int): Numeric value
            name (str, optional): String representation
        """

from schematics.models import Model
from schematics.types import StringType, IntType, BooleanType
from schematics.role import Role

class User(Model):
    name = StringType(required=True)
    email = StringType(required=True)
    age = IntType()
    is_admin = BooleanType(default=False)
    salary = IntType()

# Define roles
public_role = Role(lambda field: field in ['name', 'age'], ['name', 'age'])
admin_role = Role(lambda field: field != 'salary', ['name', 'email', 'age', 'is_admin'])

user = User({
    'name': 'John Doe',
    'email': 'john@example.com', 
    'age': 30,
    'is_admin': False,
    'salary': 75000
})

# Export with role filtering
public_data = user.export(role=public_role)
# {'name': 'John Doe', 'age': 30}

admin_data = user.export(role=admin_role)  
# {'name': 'John Doe', 'email': 'john@example.com', 'age': 30, 'is_admin': False}

from schematics.util import import_string, listify

# Dynamic import of field types
field_class = import_string('schematics.types.StringType')
field = field_class(required=True, max_length=100)

# Convert various inputs to lists
single_value = listify('item')          # ['item']
multiple_values = listify(['a', 'b'])   # ['a', 'b']
tuple_values = listify(('x', 'y'))      # ['x', 'y']

import threading
from schematics.util import get_ident

class ThreadSafeModel(Model):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._thread_id = get_ident()
    
    def validate(self, *args, **kwargs):
        current_thread = get_ident()
        if current_thread != self._thread_id:
            # Handle cross-thread validation
            pass
        return super().validate(*args, **kwargs)

from schematics.util import Constant

# Define custom export levels
BASIC_EXPORT = Constant(5, 'BASIC_EXPORT')
DETAILED_EXPORT = Constant(15, 'DETAILED_EXPORT')
FULL_EXPORT = Constant(25, 'FULL_EXPORT')

class Product(Model):
    name = StringType(export_level=BASIC_EXPORT)
    description = StringType(export_level=DETAILED_EXPORT)
    internal_notes = StringType(export_level=FULL_EXPORT)

# Export at different levels
product = Product({
    'name': 'Widget',
    'description': 'A useful widget', 
    'internal_notes': 'Manufactured in facility B'
})

# Only exports fields with export_level <= specified level
basic = product.export(export_level=BASIC_EXPORT)
# {'name': 'Widget'}

detailed = product.export(export_level=DETAILED_EXPORT)  
# {'name': 'Widget', 'description': 'A useful widget'}

full = product.export(export_level=FULL_EXPORT)
# {'name': 'Widget', 'description': 'A useful widget', 'internal_notes': 'Manufactured in facility B'}