Making Python RegEx use variables for string expressions

I have a .csv file with 开发者_运维问答the regular expression patterns that I want to match as well as the replacement patterns that I want. Some are extremely simple, such as "." -> "" or "," -> "".

When I run the following code, however, it doesn't seem to recognize the variables and the pattern is never matched.

                f = open('normalize_patterns.csv', 'rU')
                c = csv.DictReader(f)
                for row in c:
                    v = re.sub(row['Pattern'],row['Replacement'],v)

Afterwards, v is never changed and I can't seem to find out why. When I run the simple case of

                v = re.sub("\.", "", v)
                v = re.sub(",", "", v)

however, all the periods and commas are removed. Any help on the issue would be amazing. Thank you in advance! (I am pretty sure that the .csv file is formatted correctly, I've run it with just the "." and "" case and it still does not work for a certain reason)

Edit: Here are the outputs of printing row. (Thanks David!)

{'Pattern': "r'(?i)&'", 'ID': '1', 'Replacement': "'and'"}
{'Pattern': "r'(?i)\\bAssoc\\b\\.?'", 'ID': '2', 'Replacement': "'Association'"}
{'Pattern': "r'(?i)\\bInc\\b\\.?'", 'ID': '3', 'Replacement': "'Inc.'"}
{'Pattern': "r'(?i)\\b(L\\.?){2}P\\.?'", 'ID': '4', 'Replacement': "''"}
{'Pattern': "r'(?i)\\bUniv\\b\\.?'", 'ID': '5', 'Replacement': "'University'"}
{'Pattern': "r'(?i)\\bCorp\\b\\.?'", 'ID': '6', 'Replacement': "'Corporation'"}
{'Pattern': "r'(?i)\\bAssn\\b\\.?'", 'ID': '7', 'Replacement': "'Association'"}
{'Pattern': "r'(?i)\\bUnivesity\\b'", 'ID': '8', 'Replacement': "'University'"}
{'Pattern': "r'(?i)\\bIntl\\b\\.?'", 'ID': '9', 'Replacement': "'International'"}
{'Pattern': "r'(?i)\\bInst\\b\\.?'", 'ID': '10', 'Replacement': "'Institute'"}
{'Pattern': "r'(?i)L\\.L\\.C\\.'", 'ID': '11', 'Replacement': "'LLC'"} 
{'Pattern': "r'(?i)Chtd'", 'ID': '12', 'Replacement': "'Chartered'"}
{'Pattern': "r'(?i)Mfg\\b\\.?'", 'ID': '13', 'Replacement': "'Manufacturing'"}
{'Pattern': 'r"Nat\'l"', 'ID': '14', 'Replacement': "'National'"}
{'Pattern': "r'(?i)Flordia'", 'ID': '15', 'Replacement': "'Florida'"}
{'Pattern': "r'(?i)\\bLtd\\b\\.?'", 'ID': '16', 'Replacement': "'Ltd.'"}
{'Pattern': "r'(?i)\\bCo\\b\\.?'", 'ID': '17', 'Replacement': "'Company'"}
{'Pattern': "r'(?i)\\bDept\\b\\.?i\\'", 'ID': '18', 'Replacement': "'Department'"}
{'Pattern': "r'(?i)Califronia'", 'ID': '19', 'Replacement': "'California'"}
{'Pattern': "r'(?i)\\bJohn\\bHopkins\\b'", 'ID': '20', 'Replacement': "'Johns Hopkins'"}
{'Pattern': "r'(?i)\\bOrg\\b\\.?'", 'ID': '21', 'Replacement': "'Organization'"}
{'Pattern': "r'(?i)^[T]he\\s'", 'ID': '22', 'Replacement': "''"}
{'Pattern': "r'(?i)\\bAuth\\b\\.?'", 'ID': '23', 'Replacement': "'Authority'"}
{'Pattern': "r'.'", 'ID': '24', 'Replacement': "''"}
{'Pattern': "r','", 'ID': '25', 'Replacement': "''"}
{'Pattern': "r'(?i)\\s+'", 'ID': '0', 'Replacement': "''"}

And here are a few lines of the csv file (Opened in TextMate)

0,r'(?i)\s+',''
1,r'(?i)&','and'
2,r'(?i)\bAssoc\b\.?','Association'
3,r'(?i)\bInc\b\.?','Inc.'

Your issue is that your pattern values are not actually the regex pattern you want, your regex pattern is wrapped in an additional string.

For example, in your dictionary you have the value "r'.'", which you are using as a pattern. You code will run re.sub("r'.'", "", v), which probably isn't what you want:

>>> re.sub("r'.'", "", "This . won't match")
"This . won't match"
>>> re.sub("r'.'", "", "This r'x' will match")
'This  will match'

To fix this you should go back to where you are adding the regex to the dictionary and stop doing whatever is causing the string wrapping. It might be something like row['Pattern'] = repr(regex).

If you need to keep the dictionary the same for reason then be very careful with eval, if the strings are coming from an untrusted source then eval is a big security risk. Use ast.literal_eval instead.

If you remove the r'' around the pattern, it will work.

So the pattern that matches . should be as simple as '\.' instead of "r'\.'"

The problem is r in your pattern is taken as a literal r instead of it raw string meaning.

So you can also try: v=re.sub(eval(row['Pattern']), row['Replacement'], v)