  
  
  def is_simple_callable(obj):
      """
      True if the object is a callable that takes no arguments.
      """
      # Bail early since we cannot inspect built-in function signatures.
 
</s> remove from rest_framework.fields import DjangoImageField, is_simple_callable
 </s> add from rest_framework.fields import (
    BuiltinSignatureError, DjangoImageField, is_simple_callable
)
class BuiltinSignatureError(Exception):
    """
    Built-in function signatures are not inspectable. This exception is raised
    so the serializer can raise a helpful error message.
    """
    pass


  
  
class BuiltinSignatureError(Exception):
    """
    Built-in function signatures are not inspectable. This exception is raised
    so the serializer can raise a helpful error message.
    """
    pass


  def is_simple_callable(obj):
      """
      True if the object is a callable that takes no arguments.
      """
      # Bail early since we cannot inspect built-in function signatures.
keep add keep keep keep keep keep
 Raise exception when field source is a built-in (#6766) 
rest_framework/fields.py