regex remove special character except first occurrence and last occurrence-CodePudding

I need to remove the special characters inside angular brackets(<>)

date = "<dd_mm_yyyy>"
date_check_pattern= re.sub("[^A-Za-z<>]","",date)

But it is not working for

date = "<dd>_<mm>_<yyyy>"
#expected output <ddmmyyyy>

How to remove this angle bracket except first and last occurrence

CodePudding user response：

You could match the whole string and capture what is between the < and >

Then do a second replacement removing all not allowed characters from the group 1 match in the first pattern.

The first pattern matches

<(.*?)> Match from <...> and capture what is in between in group 1
(?= Positive lookahead, assert what is to the right is
- [^\s<>]*$ Optionally match any char except < or > till the end of the string
) Close the lookahead

Regex demo

The negated character class [^A-Za-z0-9] in the second sub means matching 1 times any character except what is listed in the character class.

Example code

import re

strings = [
    "<dd>_<mm>_<yyyy>",
    "<dd_mm_yyyy>",
    "<01>_<01>_<2022>",
    "file_name<dd>_<mm>_<yyyy>.csv",
    "file_name<01>_<01>_<2022>.csv",
    "file_name_<dd>_<mm>_<yyyy>_anything.csv"
]

for s in strings:
    print(
        re.sub(
            r'<(.*?)>(?=[^\s<>]*$)',
            lambda x: f"<{re.sub(r'[^A-Za-z0-9] ', '', x.group(1))}>",
            s
        )
    )

Output

<ddmmyyyy>
<ddmmyyyy>
<01012022>
file_name<ddmmyyyy>.csv
file_name<01012022>.csv
file_name_<ddmmyyyy>_anything.csv

CodePudding user response：

This might not be exactly what you want but if the characters always come at the start and the end of the line then you can use a negative lookbehind and a negative lookahead to not match the characters at start or end

import re

date = "<dd_mm_yyyy>"
date_check_pattern = re.sub("(?<!^)[^A-Za-z<>](?!$)","",date)
print(date_check_pattern)

output

<ddmmyyyy>

CodePudding user response：

I suggest you do not use Regex for this. You can use the following function and also customize specialChar

def removeSpecialChar(date):
    result = ""
    open = False
    specialChar = "_<>"
    index = 0

    lastClose = len(date)-date[::-1].find(">")-1 if date[::-1].find(">") != -1 else None
    if not lastClose: return date

    for c in date:
        if not open and c == "<":
            open = True
            result  = c
        elif open and c == ">" and index==lastClose : open = False

        if open and c not in specialChar:
            result  = c
        elif not open:
            result  = c

        index =1

    return result

example

>>> removeSpecialChar("<dd>_<mm>_<yyyy>")
"<ddmmyyyy>"

>>> removeSpecialChar("Date: (<dd>_<mm>_<yyyy>)")
"Date: (<ddmmyyyy>)"