在Python中使用正则表达式获取字符之前/之后的单词

Question

This is supposed to be easy using capturing groups, but I am not getting the correct words. I have been using the following:

#Before
print(re.sub(r'\b([A-Za-z0-9]+)\b(?=\.?\s*(\&|\-|and))',r'\1','A. & B.',flags=re.IGNORECASE))
A. & B.

#After
print(re.sub(r'(\&|\-|and)\s*\b([A-Za-z0-9]+)\b',r'\2','A. & B.',flags=re.IGNORECASE))
A. B.

The string can be one of the following:

A. - B.
A.-B.
A. & B.
A.&B.
A. AND B.

The idea is to get the word before/after of ampersand| hyphen | and ampersand| hyphen | and ampersand| hyphen | and I divided in two regex to get both words. In this example, before would get just A and the after B .

Why the capturing groups are not printing A and B in the previous examples?

Thanks in advance :)

Answer 1

The string '\\1' is octal for the decimal value 1 or 0x01 hex.

>>> import re
>>> re.sub(r'\b([A-Za-z0-9]+)\b(?=\.?\s*(\&|\-|and))','\1','A. & B.',re.IGNORECASE)
'\x01. & B.'

Regex needs backreferences to be escaped.

Either of these replacement strings refer to capture group 1
'\\\\r'

>>> import re
>>> re.sub(r'\b([A-Za-z0-9]+)\b(?=\.?\s*(\&|\-|and))','\\1','A. & B.',re.IGNORECASE)
'A. & B.'

Or,

r'\\1'

>>> import re
>>> re.sub(r'\b([A-Za-z0-9]+)\b(?=\.?\s*(\&|\-|and))',r'\1','A. & B.',re.IGNORECASE)
'A. & B.'

Answer 2

Use re.search() instead and group the desired words before and after one of the options &,-,and :

text = re.search('(\w+)\.+\s*[\&*\-*AND*and*]*\s*(\w+)\.+', 'A. & B.')
print (text.groups())