Python正则表达式可用于动态匹配组对象

Question

I'm trying to extract few interested fields from an output using Regular expression in python.

Assuming my string as

Interface1 is down (Administratively down)

The regular expression that i have written is:

pat = 'Interface(\d) is (\S)+ (.*)'

and i was able to get the required fields but when the interface is up, there will not be reason printed and i wanted to get the regex work for that case too.. right now with the regular exp that i have written, it does not seem to work.. can someone pls help..

When the interface is up, the output would be

Interface1 is Up
m.group()

Traceback (most recent call last):
  File "<pyshell#38>", line 1, in <module>
    m.group()
AttributeError: 'NoneType' object has no attribute 'group'

Answer 1

You need to remove the space between the second and last capturing group in order to match both. Also, the + operator outside of the group makes it a repeating group; place it inside instead.

Interface(\d+) is (\S+)(.*)

Regex101

Answer 2

The error message is because when the string is Interface1 is Up , your regex regex expects atleast two spaces after the substring is

>>> s1 = "Interface1 is down (Administratively down)"
>>> s2 = "Interface1 is Up"
>>> re.match(r'^Interface(\d) is (\S+)(?: (.+))?$', s1).groups()
('1', 'down', '(Administratively down)')
>>> re.match(r'^Interface(\d) is (\S+)(?: (.+))?$', s2).groups()
('1', 'Up', None)

In regex (?:....) called non-capturing group and (...) called captuirng group . ? quantifier (which is not present just after to + or * ) would turn the previous token as optional one. So (?: (.+)) is an optional one. space inside the non-capturing group matches a single space and the (.+) captures all the remaining one or more characters to another group.