Removing duplicate instances of a character using a regex expression using python

Question

This is what I tried:

(.)(?=.*\1)

This removes all instances of duplicates and leaves only the last instance, ie.

telnet -> lnet

I want this result:

telnet -> teln

How do I do this? I tried looking behind, but that only accepts a fixed length as far as I know.

Need to find a REGEX for this. I know other methods to achieve this without regex

I just want to know if it's possible. I think it's possible in .NET, but in python, could not think of a regex. The straightforward approach is simple enough, this is out of curiosity. — NobleSiks
– NobleSiks, Commented Dec 10, 2016 at 4:29
@TigerhawkT3 Would you be so kind as to unmark my question as a duplicate, or even better, link it to a more appropriate duplicate if it exists. — NobleSiks
– NobleSiks, Commented Dec 10, 2016 at 4:41
According to this, there's no single regex operation to do this. — TigerhawkT3
– TigerhawkT3, Commented Dec 10, 2016 at 4:51

vks · Accepted Answer · 2016-12-10 06:10:45Z

1

Pure regex solution is not possible.You can try with callback function though.

z=[]
def fun(matchobj):
    if matchobj.group(1) in z or matchobj.group(2) in z:
        return ''
    else:
        if matchobj.group(1):
             z.append(matchobj.group(1))
        else:
             z.append(matchobj.group(2))
        return z[-1]



x="telnet"
print re.sub(r"(.)(?=.*\1)|(.)", fun, x)

answered Dec 10, 2016 at 6:10

vks

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jwdasdk · Accepted Answer · 2016-12-10 06:25:28Z

1

a little 'hack' would be ... to reverse the string before and after the lookahead

import re

expr = r'telnetrer'[::-1]
pr = re.sub(r'(.)(?=.*\1)', r'', expr)[::-1]

print(pr)

Output

>>> telnr

answered Dec 10, 2016 at 6:25

jwdasdk

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