参考re.sub。中的事件

Question

I'm used to using re.sub() to replace letters in a string, but what about just inserting something?

import re
re.sub('Item', '- <thing>', 'A list of things: \nItem 1 \nItem 2')

should return

"A list of things: \n- Item 1 \n- Item 2"

It didn't really substitute, but rather it inserted something. Is this actually possible in regexes or should I just stick to looping through the entire text and using .replace() ? I need to replace a pattern of specific things so using lots of .replace() seems a bit inelegant.

Answer 1

You're looking for "backreferences". They are normally spelled \\X where "X" is the number of the capturing group you're referring back to (though you can also use named capturing groups, if you want to get more fancy).

Here's how you can make your code work:

re.sub(r'(Item)', r'- \1', 'A list of things: \nItem1, \nItem2')

Answer 2

Why not just make the second argument - Item ?

>>> re.sub('Item', '- Item', 'A list of things: \nItem 1 \nItem 2')
'A list of things: \n- Item 1 \n- Item 2'

Answer 3

Here's a fancy way, for the fancy inclined:

import re
re.sub('(?=Item)', '- ', 'A list of things: \nItem 1 \nItem 2')
#>>> 'A list of things: \n- Item 1 \n- Item 2'

This searches for (?=Item) , which is an empty string followed by Item and replaces it with - .

Note that in real life this should be spelt:

'A list of things: \nItem 1 \nItem 2'.replace('Item', '- Item')

although I'll assume that's just 'cause this is oversimplified.

Answer 4

This code works fine:

import re

text = re.sub(r'(Item)', '- \g<1>', 'A list of things: \nItem 1 \nItem 2')
print text

Good luck!