我的测试结果

$ python3.9
Python 3.9.5 (default, May 3 2021, 19:12:05)
[Clang 12.0.5 (clang-1205.0.22.9)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>> import re
>>>
>>> s = 'abc 456 def'
>>>
>>> re.search('\d\d\d', s)
<re.Match object; span=(4, 7), match='456'>
>>> re.search('\d{3}', s)
<re.Match object; span=(4, 7), match='456'>
>>> re.search('[0-9]{3}', s)
<re.Match object; span=(4, 7), match='456'>
>>>
>>> re.search(r'\d\d\d', s)
<re.Match object; span=(4, 7), match='456'>
>>> re.search(r'\d{3}', s)
<re.Match object; span=(4, 7), match='456'>
>>> re.search(r'[0-9]{3}', s)
<re.Match object; span=(4, 7), match='456'>
>>>