# documentación de Django - 1.10.7

# Código fuente para django.contrib.postgres.functions

    from django.db.models import DateTimeField, Func

    class TransactionNow(Func):
        template = 'CURRENT_TIMESTAMP'

        def __init__(self, output_field=None, **extra):
            if output_field is None:
                output_field = DateTimeField()
            super(TransactionNow, self).__init__(output_field=output_field, **extra)