如何在Python中使用正则表达式匹配字符串？请用1个例子来解释。回答中必须包含"At first"、"pattern"两个词汇，回答长度不超过150个字符。同时请确保回答内容不要求任何导入额外的程序包。
user
At first, you can use Python's `re` module to match patterns in strings. Example: `re.match(pattern, 'Hello World')` checks if the pattern matches at the start.
assistant