Lookahead | Very simple implementation of lookahead optimizer in pytorch | Machine Learning library
kandi X-RAY | Lookahead Summary
kandi X-RAY | Lookahead Summary
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Trending Discussions on Lookahead
QUESTION
I was taking freecodecamp.org course on JavaScript data structures, going through the RegExp chapter. I then came across the following assertion:
"The regular expression /(?=\w{3,6})(?=\D*\d)/
will check whether a password contains between 3 and 6 characters and at least one number".
(Here "check" meaning that regExp.test(password)
returns true)
This seems odd to me. First of all, looking around in Stack Exchange, I found in this post that states that A(?=B) is the definition of positive lookahead, and it makes no mention that A (the preceeding expression in the parenthesis) is optional. So, shouldn't freecodecamp's example have an expression before the first lookahead?
I believe that this another example is quite similar to the previously mentioned, but simpler so I will mention it in case the explanation is simpler, too:
Why does (?=\w)(?=\d)
, when checked against the string "1", returns true?, Shouldn't it look for an alphanumeric character followed by a numeric character?
PS: After a thought, I hypothesized that my first example checks both lookahead patterns independently (i.e. first it checks whether the string is made of three to six characters, returns true, then checks whether there is an alpha numeric character, and finally since both searchings returned true, the whole regexp test returns true). But this doesn't seem to be coherent with the definition mentioned in the post I've linked. Is there a more general definition or algorithm which the computer "internally" uses to deal with lookaheads?
...ANSWER
Answered 2021-Jun-14 at 16:03Lookaround
are similar to word-boundary metacharacters like \b
or the anchors ˆ
and $
in that they don’t match text, but rather match positions within the text.
Positive lookahead
peeks forward in the text to see if its subexpression can match, and is successful as a regex component if it can. Positive lookahead
is specified with the special sequence (?=...)
.
An important thing to understand about lookaround
constructs is that although they go through the motions to see if their subexpression is able to match, they don’t actually “consume” any text.
QUESTION
I'm trying to create a regex expression for use with Notepad++ to look for a specific character anywhere in the line but not capture it while still capturing what I want to find later in the string.
A sample of what I'm looking at is this:
...ANSWER
Answered 2021-Jun-13 at 18:05You can use
QUESTION
I'm trying to capture the show name, episode number, episode title, and resolution if present. Standard def episodes in my collection don't have a resolution suffix.
For the given samples:
...ANSWER
Answered 2021-Jun-13 at 16:21You can use
QUESTION
My problem: I use Sigil to edit xhtml files of an ebook.
When exporting from InDesign to ePub I tick option to remove forced line breaks.
This act removes all -
hyphen characters which are auto-generated by InDesign, but the characters which were added manually during my word-break fine-tune remain in the text.
Current ability of Sigil search: searching by -
parses everything, including css class names.
TODO: How to construct regex query which finds the -
within the text, but not in the html code?
Thank you!
What I have already tried: https://www.mobileread.com/forums/showpost.php?p=4099971&postcount=169
:
Here is a simple example to find the word "title" not inside a tag itself, here is the simplest regex search I could think of off the top of my head. It assumes there is no bare text in the body tag and that the xhtml is well formed.
I tried it and it appears to work. There are probably better more exhaustive regex, that can handle even broken xhtml.
Code:
...ANSWER
Answered 2021-Jun-06 at 10:42In Sigil, PCRE regex engine is used.
Thus, you can use
QUESTION
I have tried to figure it out but couldn't find a solution myself. I want to write a regex for Javascript that matches everything unless it is followed by a hyphen. So if I match among:
...ANSWER
Answered 2021-Jun-05 at 00:55In regex, you can use the metacharacter \b to designate word boundaries. I have not yet had a case use for it, although I recently noticed the feature as a useful one. Sure enough, one of its use cases is listed for purposes as follows: "Between two characters in the string, where one is a word character and the other is not a word character." This is according to website https://www.regular-expressions.info/wordboundaries.html, which is fairly consistent with overviews on the standard documentation pages for applying Javascript regex.
QUESTION
I have a string of text:
...ANSWER
Answered 2021-Jun-04 at 18:49Use
QUESTION
I have the following javascript code
...ANSWER
Answered 2021-Jun-01 at 20:18The are more ways to match a string in JavaScript, and even more ways to break the pattern as this is very very brittle.
For the example data in the question, using a negative lookahead to assert that the next line does not start with the .map
part or a string:
QUESTION
Hello stackoverflowers,
i couldn't figure the solution out by myself and couldn't find a related answer so i seek your help :)
I'm working in a VB.Net 4.x environment where i usualy have to join windows styled paths from various sources that are very unreliable in its format (leading slashes, ending slashes, sometimes double slashes inside) hence i can't use Path.Join
My next best guess is to regex replace any double occurance of a backward slash with a single one:
\\+
which is too naive, as it also converts a server adress which starts with a leading double backslash.
pseudocode
...ANSWER
Answered 2021-May-31 at 14:47You can use
QUESTION
I have to construct a regex that matches client codes that look like:
- XXX/X{3,6}
- XXX.X{3,6}
- XXX.X{3,6}/XXX
With X a number between 0 and 9.
The regex needs to be strong enough so we don't extract codes that are within another string. The use of word boundaries was my first idea.
The regex looks like this: \b\d{3}[\.\/]\d{3,6}(?:\/\d{3})?\b
The problem with word boundaries is that it also matches dots. So a number like "123/456.12" would match "123/456" as the client number. So then I came up with the following regex: (?. It uses lookbehind and lookahead and checks if that character is a white space. This matches most of the client codes correctly.
But there is still one last issue. We are using a Google OCR text to extract the codes from. This means that a valid code can be found in the text like 123/456\n
, \n123/456
, \n123/456\n
, etc. Checking if the previous and or next characters are white space doesn't work because the literal "\n" is not included in this. If I do something like (? as the word boundary it also includes a back and/or forward slash for some reason. Currently I came up with the following regex (?, but that only checks if the previous character is a "n" or white space and the next a backslash or white space. So strings like "lorem\123/456" would still find a match. I need some way to include the "\n" in the white space characters without breaking the lookahead/lookbehind.
Do you guys have any idea how to solve this issue? All input is appreciated. Thx!
...ANSWER
Answered 2021-May-31 at 10:58It seems you want to subtract \n
from the whitespace boundaries. You can use
QUESTION
i am struggling with RegEx, i want to target all elements in a text that have ";" or "?" or ":" or "!", and then i want to split that text according to theses elements . So it it like doing myText.split('?') and myText.split(';') and myText.split(':')..but ALL at the same time using a regex rule.
it is quite easy and theses special characters stand on their own, all i have to do is :
...ANSWER
Answered 2021-May-30 at 04:57It sounds like you want to split some input text based on sentences. One option would be a find all approach using match
. This avoids the needs for a lookbehind.
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Install Lookahead
You can use Lookahead like any standard Python library. You will need to make sure that you have a development environment consisting of a Python distribution including header files, a compiler, pip, and git installed. Make sure that your pip, setuptools, and wheel are up to date. When using pip it is generally recommended to install packages in a virtual environment to avoid changes to the system.
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