Patched code sample

# Simplified from calibre.utils.formatter
class Formatter:
    def __init__(self, user_data, allow_python_templates=None):
        self.user_data = user_data
        # The default of `None` is permissive due to the check `is not False`
        self.allow_python_templates = allow_python_templates

    def compile_python_template(self, template):
        # In a real scenario, this would compile and run Python code.
        pass

    def format(self, template, data):
        # Simplified evaluation logic for demonstration.
        if template.startswith('python:'):
            if self.allow_python_templates is not False:
                return self.compile_python_template(template)
            raise ValueError('Python templates not allowed')

        if template.startswith('template('):
            sub_template = template[9:-1]
            return self.fn_template(data, sub_template)
        
        return "processed"

    def fn_template(self, data, *args):
        # FIX: The `allow_python_templates` setting is inherited by the new
        # formatter, preserving the security context.
        formatter = Formatter(self.user_data, allow_python_templates=self.allow_python_templates)
        return formatter.format(args[0], data)