Regular expression substitution Python

Question

I am having trouble with this one. I am trying to get a better handle on RE but it is not working. I have a list of strings that I want to erase if they are found in another string.

this is the exclusion list:

exclusionList = ['\+','of','<ET>f.','to','the','<L>L.</L>','f.','in','and','see','a','<L>Fr.</L>','as','<ET>ad.','<ET>a.','<PS>v.</PS></XR>',
             'from','<CF>ab</CF>','or','n.','<L>OFr.</L>','pple.','away','was','with','off,','pa.','on','is','cf.','stem','ad.','which',
             'by','action','ppl.','Cf.','but','<L>Gr.</L>','be','after','=','The','form','for','an','<XR><RX>prec.</RX></XR>',
             '<PS>a.</PS></XR>','<L>Eng.</L>','<PS>pref.</PS>','also','L.</L>','<XR><XL>a-</XL>','<XR><XL>-ing</XL><HO>1</HO></XR>.</ET>',
             'vb.','See','In','<L>OE.</L>','used','it','see','this','not','<PS>prep.</PS><HO>1</HO></XR>','has','a','so','early','s']

And this is what I am using to remove those words:

first_word = re.sub(r'\b'+exclusionList[a]+'\b', '',first_word)

where first word is a string read from a text file. I know this is going to be simple but I just do not quite get how to use RE very well.

Thanks

Answer 1

I can only guess, but probably you want something like this:

pattern = r'\b({})\b'.format('|'.join(map(re.escape, exclusionList)))
first_word = re.sub(pattern, '', first_word)

Note that I'm escaping the words, so they will be matched literally, instead of being interpreted as regular expressions (which they don't seem to be).

Answer 2

This should do the trick all at once:

exclusionRegex = r'\b(' + '|'.join(re.escape(word) for word in exclusionList) + r')\b'
first_word = re.sub(exclusionRegex, '', first_word)

EDIT : This is my test script:

import re

exclusionList = ['\+','of','<ET>f.','to','the','<L>L.</L>','f.','in','and','see','a','<L>Fr.</L>','as','<ET>ad.','<ET>a.','<PS>v.</PS></XR>',
             'from','<CF>ab</CF>','or','n.','<L>OFr.</L>','pple.','away','was','with','off,','pa.','on','is','cf.','stem','ad.','which',
             'by','action','ppl.','Cf.','but','<L>Gr.</L>','be','after','=','The','form','for','an','<XR><RX>prec.</RX></XR>',
             '<PS>a.</PS></XR>','<L>Eng.</L>','<PS>pref.</PS>','also','L.</L>','<XR><XL>a-</XL>','<XR><XL>-ing</XL><HO>1</HO></XR>.</ET>',
             'vb.','See','In','<L>OE.</L>','used','it','see','this','not','<PS>prep.</PS><HO>1</HO></XR>','has','a','so','early','s']

exclusionRegex = r'\b(' + '|'.join(re.escape(word) for word in exclusionList) + r')\b'
first_word = 'This is a test of the regex'
print re.sub(exclusionRegex, '', first_word)

And this is the output:

This test regex