正则捕获

目的： 给表达式 '10+6/5-4*2' 中每个运算符左右都加一个空格字符，变成：'10 + 6 / 5 - 4 * 2'

思路： 分组、捕获、替换

1. 替换字符中含参数 1 （此处不能叫参数，想不到叫什么，那就不管它~~）

>>> bds = '10+6/5-4*2' # 表达式
>>> m = re.sub(r'([*+-/])', ' 1 ', bds) # 注意1左右皆有一个空格！！
>>> m
 '10 + 6 / 5 - 4 * 2'

2. 替换字符中含参数 g<1>

>>> bds = '10+6/5-4*2' # 表达式
>>> m = re.sub(r'([*+-/])', ' g<1> ', bds)
>>> m
 '10 + 6 / 5 - 4 * 2'

3. 模式中也可含参数 1

>>> greed = "Hello Jack! Are you OK, Jack?"
>>> m = re.sub(r"Hello (w+)! Are you OK, 1?", "g<1>", greed)
>>> m
"Hello Jack! Are you OK, Jack?"

4. 模式中也可含参数 ：命名组 (?P=yourname)

>>> greed = "Hello Jack! Are you OK, Jack?"
>>> m = re.sub(r"Hello (?P<yourname>w+)! Are you OK, (?P=yourname)?", "g<yourname>", greed)
>>> m
"Hello Jack! Are you OK, Jack?"