Special characters replace using regex in python

Question

Just for learning I am trying to replace all the special characters present in the keyboard to replace with underscore'_'

List of characters= ~!@#$%^&*()+|}{:"?><-=[]\;',./

string I created:

table = """123~!@#$%^&*()+|}{:"?><-=[]\;',./"""

import re

table1= re.sub(r'!~@#$%^&*()-+={}[]:;<.>?/\'"', '_', table)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/re.py", line 151, in sub
    return _compile(pattern, flags).sub(repl, string, count)
  File "/usr/lib64/python2.7/re.py", line 242, in _compile
    raise error, v # invalid expression
sre_constants.error: unexpected end of regular expression

Unable to do so I am getting the above error.

How can I replace the special characters in the string using regex

Is that your exact string? It does not have any quotes. Try table = """...""" Also, what's with the 123 at the beginning? — tobias_k
– tobias_k, Commented Nov 14, 2017 at 21:02
Note that )-+ creates an invalid range. Always put the - at the end/start of the character class. Yeah, and use a character class :) — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 14, 2017 at 21:02
@tobias_k yes it is the exact string and nothing in front of 123 — User12345
– User12345, Commented Nov 14, 2017 at 21:04
There's also \W, which matches-all non-word characters: re.sub(r'\W', '_', some_string). docs.python.org/3/library/re.html#regular-expression-syntax — user8651755
– user8651755, Commented Nov 14, 2017 at 21:17
@Blurp Good point, but that would also replace e.g. whitespace. Might use something like [^\w\s] though, depending on what exactly OP wants to replace. Also, there seem to be chars like | what shall not be replaced (might be a mistake in the question, though). — tobias_k
– tobias_k, Commented Nov 14, 2017 at 21:23

tobias_k · Accepted Answer · 2017-11-14 21:08:33Z

2

You could use re.escape to escape all the special regex characters in the string, and then enclose the escaped string into [...] so it matches any of them.

>>> re.sub("[%s]" % re.escape('!~@#$%^&*()-+={}[]:;<.>?/\''), '_', table)
'123____________|___"_______\\__,__'

However, as you are not really using that regex as a regex, you might instead just check whether each character is in that string:

>>>''.join("_" if c in '!~@#$%^&*()-+={}[]:;<.>?/\'' else c for c in table)
'123____________|___"_______\\__,__'

Or to make the lookup a bit faster, create a set from the chars in that string first:

>>> bad_chars = set('!~@#$%^&*()-+={}[]:;<.>?/\'')
>>> ''.join("_" if c in bad_chars else c for c in table)

answered Nov 14, 2017 at 21:08

tobias_k

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Jan · Accepted Answer · 2017-11-14 21:10:46Z

1

Just put it in a character class and rearrange the position of some characters (namely -, escaping +):

import re
table = """123~!@#$%^&*()+|}{:"?><-=[]\;',./"""

table1 = re.sub(r'[-\+!~@#$%^&*()={}\[\]:;<.>?/\'"]', '_', table)
print(table1)
# 123____________|___________\__,__

answered Nov 14, 2017 at 21:10

Jan

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