请问python里面的@什么意思？

比如

Python code:
@orm.validates('title')
def validate_title(self, key, title):
"""Assure that page titles are wikiwords and valid length"""
if len(title) > 40:
raise ValueError('Page title must be 40 characters or fewer')
if not wikiwords.match(title):
log.warning('%s: invalid title (%s)' % (self.__class__.__name__,
title))
raise ValueError('Page title must be a wikiword (CamelCase)')
return title

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感谢～