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Remove specific combination of characters in dataframe colum?

I have the following issue where I have some data that has a specific combination of characters that I need to remove, example:
data_col
*.test1.934n
test1.tedsdh
*.test1.test.sdfsdf
jhsdakn
*.test2.test
What I need to remove is all the instances that exist for the "*." character combination in the dataframe. So far I've tried:
df['data_col'].str.replace('^*.','')
However when I run the code it gives me this error:
re.error: nothing to repeat at position 1
Any advise on how to fix this? Thanks in advance.

The default behaviour of .str.replace in pandas version 1.4.2 or earlier is to treat the replacememnt pattern as a regular expression. If you are using regular expressions to match characters with special meaning like * and . you have to escape them with backslashes:
df['data_col'].str.replace(r'^\*\.', '', regex=True)
Note that I used raw string literals to make sure that backslashes are treated as is. I also added regex=True, because otherwise pandas complains that in future it will not treat patterns as regex. Due to ^ at the beginning, this regex will only match the beginning of each string.
However, it is also possible that you don't need regular expressions in this particular case at all.
If you want to remove any instance of *. in your strings (not only the beginning ones), you can just do it with
df['data_col'].str.replace('*.', '', regex=False)
If you want to remove instance of *. only at the beginning of the string, you can use .removeprefix instead:
df['data_col'].str.removeprefix('*.')

Python Regex; why does ignorecase change something? [duplicate]

$.validator.addMethod('AZ09_', function (value) {
return /^[a-zA-Z0-9.-_]+$/.test(value);
}, 'Only letters, numbers, and _-. are allowed');
When I use somehting like test-123 it still triggers as if the hyphen is invalid. I tried \- and --

Escaping using \- should be fine, but you can also try putting it at the beginning or the end of the character class. This should work for you:
/^[a-zA-Z0-9._-]+$/

Escaping the hyphen using \- is the correct way.
I have verified that the expression /^[a-zA-Z0-9.\-_]+$/ does allow hyphens. You can also use the \w class to shorten it to /^[\w.\-]+$/.
(Putting the hyphen last in the expression actually causes it to not require escaping, as it then can't be part of a range, however you might still want to get into the habit of always escaping it.)

The \- maybe wasn't working because you passed the whole stuff from the server with a string. If that's the case, you should at first escape the \ so the server side program can handle it too.
In a server side string: \\-
On the client side: \-
In regex (covers): -
Or you can simply put at the and of the [] brackets.

Generally with hyphen (-) character in regex, its important to note the difference between escaping (\-) and not escaping (-) the hyphen because hyphen apart from being a character themselves are parsed to specify range in regex.
In the first case, with escaped hyphen (\-), regex will only match the hyphen as in example /^[+\-.]+$/
In the second case, not escaping for example /^[+-.]+$/ here since the hyphen is between plus and dot so it will match all characters with ASCII values between 43 (for plus) and 46 (for dot), so will include comma (ASCII value of 44) as a side-effect.

\- should work to escape the - in the character range. Can you quote what you tested when it didn't seem to? Because it seems to work: http://jsbin.com/odita3

A more generic way of matching hyphens is by using the character class for hyphens and dashes ("\p{Pd}" without quotes). If you are dealing with text from various cultures and sources, you might find that there are more types of hyphens out there, not just one character. You can add that inside the [] expression

REGEX in Python: what's wrong with (?<!\\)\".+(?<!\\)\"?

trying to parse JSON key names within quotes, including escaped quotes.
my thinking is: take anything between quotes not prefixed with \
(?<!\\)\".+(?<!\\)\"
where (?<!\\)\" should screen for " but not \" but Python complains about unbalanced parenthesis.
if I use (?<!\\\)\" Python is happy , but this doesn't work:
re.findall('(?<!\\\)\".+(?<!\\\)\"','"this is \"the\". key"."and this.is.the.child"')
leads:
['"this is "the". key"."and this.is.the.child"']
when I expect:
['"this is "the". key"', '"and this.is.the.child"']
split at the dot which is enclosed with " without escape.
I feel like i need an 'anything but not escaped double quote ' in the middle, but if
[^"] screens for anything but a double quote, I don't know how to negate the (?<!\\\)\" expression within a [ ] set that takes characters as literals.
i would want something like [^(?<!\\\)\"] but that doesn't work.
I tried things like [[^"]|(\")]+ (anything but a double quote, or a \" ) but that doesn't seem to work either...
Can;t seem to find the right way to do this...
Any ideas?
Thanks for help
EDIT:
My real goal is to be able to split full 'text' JSON key names to transform them into alphanum only values. The transform is irrelevant here, but the goal is to split the keys to represent the hierarchy properly. The keys are in text form.
EDIT 2:
even though OmnipotentEntity is most likely right, writing a parser will have to wait..
This solution below doesn't support the "\" or "\\" cases as indicated in his comments.
I settled with
"(?:\\"|[^"])*?"|(?<=\.)[^".]+?(?=\.)|^[^".]+?(?=\.)|(?<=\.)[^".]+?$
inspired by the answer from Avinash Raj
but adding support for keys that are not enclosed in double quotes:
no quotes beginning of line ending with .
.key.
and
.lastkey
when substituting [empty] with the same regex, one should find 1 less element than the number of found strings, or there is an error.
something like .. outside "" will fail that test

Fundamentally, using a regular expression to match quoted strings is impossible in the general case. JSON is not a regular language (all regular languages are LL(1) but not all LL(1) languages are regular, JSON is one of these), so it cannot be matched by a regular expression.
Avinash Raj's regular expression (?<!\\)".*?(?<!\\)", for instance, fails on the the case "\\". Because the quote is preceded by a \ but the backslash doesn't function as an escape. But you can't special case this situation because then "\\\"" will fail. And if you special case this situation, you can just use 4 \ and then 5 \ etc.
Lookbehinds aren't part of standard regular expressions so they can match more grammars than simply regular ones. So you might be able to come up with a regular expression that works in this case. However, I would recommend writing a parser instead, they are very easy to do for LL(1) grammars. It will be easier, more understandable, less brittle, and give you more leverage to deal with non-conformant JSON and give you the ability to write better diagnostic messages in this case.

Try to define your regex as raw string notation.
>>> s = r'"this is \"the\". key"."and this.is.the.child"'
>>> re.findall(r'"(?:\\"|[^"])*?"', s)
['"this is \\"the\\". key"', '"and this.is.the.child"']
DEMO
OR
>>> re.findall(r'(?<!\\)".*?(?<!\\)"', s)
['"this is \\"the\\". key"', '"and this.is.the.child"']
(?<!\\) called negative lookbehind which asserts that the match won't be preceded by a backslash.
" Matches a double quotes.
.*?(?<!\\)" Matches all the characters non-greedily upto the double quotes which is not preceded by a backslash.

Can vim substitute a special python expression as a whole raw sentence?

I got a expression like:
int(i[10])
I want to change this as a whole into
int(arg_dict["count"])
both have lots of special characters.
Is there a way that I can ignore all its special characters in these two stuff and treat them as raw material in vim ?
for example, I want to make the following block work with your answer
:%s/#your answer# int(i[10])/#your answer# int(arg_dict["count"])

The only "special" characters, here, are [] so they are the only ones you need to escape:
:s/int(i\[10\])/int(arg_dict["count"])/g
If you want to make use of capturing you will need to escape the () of the capture group as well:
:s/\(int(\)i\[10\])/\1arg_dict["count"])/g

Trying to find all instances of a keyword NOT in comments or literals?

I'm trying to find all instances of the keyword "public" in some Java code (with a Python script) that are not in comments or strings, a.k.a. not found following //, in between a /* and a */, and not in between double or single quotes, and which are not part of variable names-- i.e. they must be preceded by a space, tab, or newline, and must be followed by the same.
So here's what I have at the moment--
//.*\spublic\s.*\n
/\*.*\spublic\s.*\*/
".*\spublic\s.*"
'.*\spublic\s.*'
Am I messing this up at all?
But that finds exactly what I'm NOT looking for. How can I turn it around and search the inverse of the sum of those four expressions, as a single regex?
I've figured out this probably uses negative look-ahead and look-behind, but I still can't quite piece it together. Also, for the /**/ regex, I'm concerned that .* doesn't match newlines, so it would fail to recognize that this public is in a comment:
/*
public
*/
Everything below this point is me thinking on paper and can be disregarded. These thoughts are not fully accurate.
Edit:
I daresay (?<!//).*public.* would match anything not in single line comments, so I'm getting the hang of things. I think. But still unsure how to combine everything.
Edit2:
So then-- following that idea, I |ed them all to get--
(?<!//).*public.*|(?<!/\*).*public.\*/(?!\*/)|(?<!").*public.*(?!")|(?<!').*public.*(?!')
But I'm not sure about that. //public will not be matched by the first alternate, but it will be matched by the second. I need to AND the look-aheads and look-behinds, not OR the whole thing.

I'm sorry, but I'll have to break the news to you, that what you are trying to do is impossible. The reason is mostly because Java is not a regular language. As we all know by now, most regex engines provide non-regular features, but Python in particular is lacking something like recursion (PCRE) or balancing groups (.NET) which could do the trick. But let's look into that in more depth.
First of all, why are your patterns not as good as you think they are? (for the task of matching public inside those literals; similar problems will apply to reversing the logic)
As you have already recognized, you will have problems with line breaks (in the case of /*...*/). This can be solved by either using the modifier/option/flag re.S (which changes the behavior of .) or by using [\s\S] instead of . (because the former matches any character).
But there are other problems. You only want to find surrounding occurrences of the string or comment literals. You are not actually making sure that they are specifically wrapped around the public in question. I'm not sure how much you can put onto a single line in Java, but if you had an arbitrary string, then later a public and then another string on a single line, then your regex would match the public because it can find the " before and after it. Even if that is not possible, if you have two block comments in the same input, then any public between those two block comments would cause a match. So you would need to find a way to assert only that your public is really inside "..." or /*...*/ and not just that these literals can be found anywhere to left of right of it.
Next thing: matches cannot overlap. But your match includes everything from the opening literal until the ending literal. So if you had "public public" that would cause only one match. And capturing cannot help you here. Usually the trick to avoid this is to use lookarounds (which are not included in the match). But (as we will see later) the lookbehind doesn't work as nicely as you would think, because it cannot be of arbitrary length (only in .NET that is possible).
Now the worst of all. What if you have " inside a comment? That shouldn't count, right? What if you have // or /* or */ inside a string? That shouldn't count, right? What about ' inside "-strings and " inside '-strings? Even worse, what about \" inside "-string? So for 100% robustness you would have to do a similar check for your surrounding delimiters as well. And this is usually where regular expressions reach the end of their capabilities and this is why you need a proper parser that walks the input string and builds a whole tree of your code.
But say you never have comment literals inside strings and you never have quotes inside comments (or only matched quotes, because they would constitute a string, and we don't want public inside strings anyway). So we are basically assuming that every of the literals in question is correctly matched, and they are never nested. In that case you can use a lookahead to check whether you are inside or outside one of the literals (in fact, multiple lookaheads). I'll get to that shortly.
But there is one more thing left. What does (?<!//).*public.* not work? For this to match it is enough for (?<!//) to match at any single position. e.g. if you just had input // public the engine would try out the negative lookbehind right at the start of the string, (to the left of the start of the string), would find no //, then use .* to consume // and the space and then match public. What you actually want is (?<!//.*)public. This will start the lookbehind from the starting position of public and look all the way to the left through the current line. But... this is a variable-length lookbehind, which is only supported by .NET.
But let's look into how we can make sure we are really outside of a string. We can use a lookahead to look all the way to the end of the input, and check that there is an even number of quotes on the way.
public(?=[^"]*("[^"]*"[^"]*)*$)
Now if we try really hard we can also ignore escaped quotes when inside of a string:
public(?=[^"]*("(?:[^"\\]|\\.)*"[^"]*)*$)
So once we encounter a " we will accept either non-quote, non-backslash characters, or a backslash character and whatever follows it (that allows escaping of backslash-characters as well, so that in "a string\\" we won't treat the closing " as being escaped). We can use this with multi-line mode (re.M) to avoid going all the way to the end of the input (because the end of the line is enough):
public(?=[^"\r\n]*("(?:[^"\r\n\\]|\\.)*"[^"\r\n]*)*$)
(re.M is implied for all following patterns)
This is what it looks for single-quoted strings:
public(?=[^'\r\n]*('(?:[^'\r\n\\]|\\.)*'[^'\r\n]*)*$)
For block comments it's a bit easier, because we only need to look for /* or the end of the string (this time really the end of the entire string), without ever encountering */ on the way. That is done with a negative lookahead at every single position until the end of the search:
public(?=(?:(?![*]/)[\s\S])*(?:/[*]|\Z))
But as I said, we're stumped on the single-line comments for now. But anyway, we can combine the last three regular expressions into one, because lookaheads don't actually advance the position of the regex engine on the target string:
public(?=[^"\r\n]*("(?:[^"\r\n\\]|\\.)*"[^"\r\n]*)*$)(?=[^'\r\n]*('(?:[^'\r\n\\]|\\.)*'[^'\r\n]*)*$)(?=(?:(?![*]/)[\s\S])*(?:/[*]|\Z))
Now what about those single-line comments? The trick to emulate variable-length lookbehinds is usually to reverse the string and the pattern - which makes the lookbehind a lookahead:
cilbup(?!.*//)
Of course, that means we have to reverse all other patterns, too. The good news is, if we don't care about escaping, they look exactly the same (because both quotes and block comments are symmetrical). So you could run this pattern on a reversed input:
cilbup(?=[^"\r\n]*("[^"\r\n]*"[^"\r\n]*)*$)(?=[^'\r\n]*('[^'\r\n]*'[^'\r\n]*)*$)(?=(?:(?![*]/)[\s\S])*(?:/[*]|\Z))(?!.*//)
You can then find the match positions in your actual input by using inputLength -foundMatchPosition - foundMatchLength.
Now what about escaping? That get's quite annoying now, because we have to skip quotes, if they are followed by a backslash. Because of some backtracking issues we need to take care of that in five places. Three times, when consuming non-quote characters (because we need to allow "\ as well now. And twice, when consuming quote characters (using a negative lookahead to make sure there is no backslash after them). Let's look at double quotes:
cilbup(?=(?:[^"\r\n]|"\\)*(?:"(?!\\)(?:[^"\r\n]|"\\)*"(?!\\)(?:[^"\r\n]|"\\)*)*$)
(It looks horrible, but if you compare it with the pattern that disregards escaping, you will notice the few differences.)
So incorporating that into the above pattern:
cilbup(?=(?:[^"\r\n]|"\\)*(?:"(?!\\)(?:[^"\r\n]|"\\)*"(?!\\)(?:[^"\r\n]|"\\)*)*$)(?=(?:[^'\r\n]|'\\)*(?:'(?!\\)(?:[^'\r\n]|'\\)*'(?!\\)(?:[^'\r\n]|'\\)*)*$)(?=(?:(?![*]/)[\s\S])*(?:/[*]|\Z))(?!.*//)
So this might actually do it for many cases. But as you can see it's horrible, almost impossible to read, and definitely impossible to maintain.
What were the caveats? No comment literals inside strings, no string literals inside strings of the other type, no string literals inside comments. Plus, we have four independent lookaheads, which will probably take some time (at least I think I have a voided most of backtracking).
In any case, I believe this is as close as you can get with regular expressions.
EDIT:
I just realised I forgot the condition that public must not be part of a longer literal. You included spaces, but what if it's the first thing in the input? The easiest thing would be to use \b. That matches a position (without including surrounding characters) that is between a word character and a non-word character. However, Java identifiers may contain any Unicode letter or digit, and I'm not sure whether Python's \b is Unicode-aware. Also, Java identifiers may contain $. Which would break that anyway. Lookarounds to the rescue! Instead of asserting that there is a space character on every side, let's assert that there is no non-space character. Because we need negative lookarounds for that, we will get the advantage of not including those characters in the match for free:
(?<!\S)cilbup(?!\S)(?=(?:[^"\r\n]|"\\)*(?:"(?!\\)(?:[^"\r\n]|"\\)*"(?!\\)(?:[^"\r\n]|"\\)*)*$)(?=(?:[^'\r\n]|'\\)*(?:'(?!\\)(?:[^'\r\n]|'\\)*'(?!\\)(?:[^'\r\n]|'\\)*)*$)(?=(?:(?![*]/)[\s\S])*(?:/[*]|\Z))(?!.*//)
And because just from scrolling this code snippet to the right one cannot quite grasp how ridiculously huge this regex is, here it is in freespacing mode (re.X) with some annotations:
(?<!\S) # make sure there is no trailing non-whitespace character
cilbup # public
(?!\S) # make sure there is no leading non-whitespace character
(?= # lookahead (effectively lookbehind!) to ensure we are not inside a
# string
(?:[^"\r\n]|"\\)*
# consume everything except for line breaks and quotes, unless the
# quote is followed by a backslash (preceded in the actual input)
(?: # subpattern that matches two (unescaped) quotes
"(?!\\) # a quote that is not followed by a backslash
(?:[^"\r\n]|"\\)*
# we've seen that before
"(?!\\) # a quote that is not followed by a backslash
(?:[^"\r\n]|"\\)*
# we've seen that before
)* # end of subpattern - repeat 0 or more times (ensures even no. of ")
$ # end of line (start of line in actual input)
) # end of double-quote lookahead
(?=(?:[^'\r\n]|'\\)*(?:'(?!\\)(?:[^'\r\n]|'\\)*'(?!\\)(?:[^'\r\n]|'\\)*)*$)
# the same horrible bastard again for single quotes
(?= # lookahead (effectively lookbehind) for block comments
(?: # subgroup to consume anything except */
(?![*]/) # make sure there is no */ coming up
[\s\S] # consume an arbitrary character
)* # repeat
(?:/[*]|\Z)# require to find either /* or the end of the string
) # end of lookahead for block comments
(?!.*//) # make sure there is no // on this line

Have you considered replacing all comments and single and double quoted string literals with null strings using the re sub() method. Then just do a simple search/match/find of the resulting file for the word you're looking for?
That would at least give you the line numbers where the word is located. You may be able to use that information to edit the original file.

You could use pyparsing to find public keyword outside a comment or a double quoted string:
from pyparsing import Keyword, javaStyleComment, dblQuotedString
keyword = "public"
expr = Keyword(keyword).ignore(javaStyleComment | dblQuotedString)
Example
for [token], start, end in expr.scanString(r"""{keyword} should match
/*
{keyword} should not match "
*/
// this {keyword} also shouldn't match
"neither this \" {keyword}"
but this {keyword} will
re{keyword} is ignored
'{keyword}' - also match (only double quoted strings are ignored)
""".format(keyword=keyword)):
assert token == keyword and len(keyword) == (end - start)
print("Found at %d" % start)
Output
Found at 0
Found at 146
Found at 187
To ignore also single quoted string, you could use quotedString instead of dblQuotedString.
To do it with only regexes, see regex-negation tag on SO e.g., Regular expression to match string not containing a word? or using even less regex capabilities Regex: Matching by exclusion, without look-ahead - is it possible?. The simple way would be to use a positive match and skip matched comments, quoted strings. The result is the rest of the matches.

It's finding the opposite because that's just what you're asking for. :)
I don't know a way to match them all in a single regex (though it should be theoretically possible, since the regular languages are closed under complements and intersections). But you could definitely search for all instances of public, and then remove any instances that are matched by one of your "bad" regexes. Try using for example set.difference on the match.start and match.end properties from re.finditer.