I'm writing a python regex formula that parses the content of a heading, however the greedy quantifier is not working well, and the non greedy quantifier is not working at all.
My string is
Step 1 Introduce The Assets:
Step2 Verifying the Assets
Step 3Making sure all the data is in the right place:
What I'm trying to do is extract the step number, and the heading, excluding the :.
Now I've tried multiple regex string and came up with these 2:
r1 = r"Step ?([0-9]+) ?(.*) ?:?"
r2 = r"Step ?([0-9]+) ?(.*?) ?:?"
r1 is capturing the step number, but is also capturing : at the end.
r2 is capturing the step number, and ''. I'm not sure how to handle the case where there is a .* followed by a string.
Necessary Edit:
The heading might contain : inside the string, I just want to ignore the trailing one. I know I can strip(':') but I want to understand what I'm doing wrong.
You can write the pattern using a negated character class without the non greedy and optional parts using a negated character class:
\bStep ?(\d+) ?([^:\n]+)
\bStep ? Match the word Step and optional space
(\d+) ? Capture 1+ digits in group 1 followed by matching an optional space
([^:\n]+) Capture 1+ chars other than : or a newline in group 2
Regex demo
If the colon has to be at the end of the string:
\bStep ?(\d+) ?([^:\n]+):?$
Regex demo
Related
Using regex (Python) I want to capture a group \d-.+? that is immediately followed by another pattern \sLEFT|\sRIGHT|\sUP.
Here is my test set (from http://nflsavant.com/about.php):
(9:03) (SHOTGUN) 30-J.RICHARD LEFT GUARD PUSHED OB AT MIA 9 FOR 18 YARDS (29-BR.JONES; 21-E.ROWE).
(1:06) 69-R.HILL REPORTED IN AS ELIGIBLE. 33-D.COOK LEFT GUARD TO NO 4 FOR -3 YARDS (56-D.DAVIS; 93-D.ONYEMATA).
(3:34) (SHOTGUN) 28-R.FREEMAN LEFT TACKLE TO LAC 37 FOR 6 YARDS (56-K.MURRAY JR.).
(1:19) 22-L.PERINE UP THE MIDDLE TO CLE 43 FOR 2 YARDS (54-O.VERNON; 51-M.WILSON).
My best attempt is (\d*-.+?)(?=\sLEFT|\sRIGHT|\sUP), which works unless other characters appear between a matching capture group and my positive lookahead. In the second line of my test set this expression captures "69-R.HILL REPORTED IN AS ELIGIBLE. 33-D.COOK." instead of the desired "33-D.COOK".
My inputs are also saved on regex101, here: https://regex101.com/r/tEyuiJ/1
How can I modify (or completely rewrite) my regex to only capture the group immediately followed by my exact positive lookahead with no extra characters between?
To prevent skipping over digits, use \D non-digit (upper is negated \d).
\b(\d+-\D+?)\s(?:LEFT|RIGHT|UP)
See this demo at regex101
Further added a word boundary and changed the lookahead to a group.
If you want a capture group without any lookarounds:
\b(\d+-\S*)\s(?:LEFT|RIGHT|UP)\b
Explanation
\b A word boundary to prevent a partial word match
(\d+-\S*) Capture group 1, match 1+ digits - and optional non whitespace characters
\s Match a single whitespace character
(?:LEFT|RIGHT|UP) Match any of the alternatives
\b A word boundary
See the capture group value on regex101.
This is why you should be careful about using . to match anything and everything unless it's absolutely necessary. From the example you provided, it appears that what you're actually wanting to capture contains no spaces, thus we could utilize a negative character class [^\s] or alternatively more precisely [\w.], with either case using a * quantifier.
Your end result would look like "(\d*-[\w.]*)(?=\sLEFT|\sRIGHT|\sUP)"gm. And of course, when . is within the character class it's treated as a literal string - so it's not required to be escaped.
See it live at regex101.com
Try this:
\b\d+-[^\r \n]+(?= +(?:LEFT|RIGHT|UP)\b)
\b\d+-[^\r \n]+
\b word boundary to ignore things like foo30-J.RICHARD
\d+ match one or more digit.
- match a literal -.
[^\r \n]+ match on or more character except \r, \n and a literal space . Excluding \r and \n helps us not to cross newlines, and that is why \s is not used(i.e., it matches \r and \n too)
(?= +(?:LEFT|RIGHT|UP)\b) Using positive lookahead.
+ Ensure there is one or more literal space .
(?:LEFT|RIGHT|UP)\b using non-caputring group, ensure our previous space followed by one of these words LEFT, RIGHT or UP. \b word boundary to ignore things like RIGHTfoo or LEFTbar.
See regex demo
I am quite new to regex and I right now Have a problem formulating a regex to match a string where the first and last letter are different. I looked up on the internet and found a regex that just does it's opposite. i.e. matches words that have same starting and ending letter. Can anyone please help me to understand if I can negeate this regex in some way or can create a new regex to match my requirements. The regex that needs to be modiifed or changed is:
^\s|^[a-z]$|^([a-z]).*\1$
This matches these Strings :
aba,
a,
b,
c,
d,
" ",
cccbbbbbbac,
aaaaba
But I want it to match strings like:
aaabbcz,
zba,
ccb,
cbbbba
Can anyone please help me in this regard? Thank you.
Note: I will be using this with Python Regex, so the regex should be compataible to be used with Python.
You don't need a regex for this, just use
s[0] != s[-1]
where s is your string. If you must use a regex, you can use this:
^(.).*(?!\1).$
This looks for
^ : beginning of string
(.) : a character (captured in group 1)
.* : some number of characters
(?!\1). : a character which is not the character captured in group 1
$ : end of string
Regex demo on regex101
This part of your pattern ^([a-z]).*\1$ only accounts for chars a-z, but you also want to exclude " "
You can rewrite that pattern by putting the part after the capture group inside a negative lookahead.
^(.)(?!.*\1$).+
^ Start of string
(.) Capture a single char (including spaces) in group 1
(?!.*\1$) Negative lookahead, assert that the string does not end with the same character
.+ Match 1+ characters so that the string has a minimum of 2 characters
See a regex demo.
If the string should start and end with a non whitespace character to prevent / trailing trailing spaces, you can start the match with a non whitespace character \S and also end the match with a non whitespace character.
^(\S)(?!.*\1$).*\S$
See another regex demo.
If I have a string eg.: 'hcto,231' or 'hcto.12' I want to be able to capture 'o,231' or 'o.12' and process it as a number ('hct' is random and any other string can replace it).
But I don't want to capture if the 'o' character if followed by a decimal number eg: 'wordo.23.12' or 'wordo,23,12'.
I've tried using the following regex:
([oO][.,][0-9]+)(?!([.,][0-9]+))
but it always matches.
In the string 'hcto.22.23' it matches the bold part, but I don't want it to match anything. Is there a way to combine groups so it won't match if the negative lookahead is true.
The match occurs in hcto.22.23 because the lookahead triggers backtracking, and since [0-9]+ match match a single 2 (it does not have to match 22) the match succeeds and returns a smaller, unexpected match:
It seems the simplest way to fix the current issue is to make the dot or comma pattern in the lookahead optional, and remove unnecessary groups:
[oO][.,]\d+(?![.,]?\d)
See the regex demo.
Details
[oO] - o or O
[.,] - a dot or comma
\d+ - one or more digits
(?![.,]?\d) - not followed with ./, and a digit, or just with a digit.
I am trying to create a regex expression in Python for non-hyphenated words but I am unable to figure out the right syntax.
The requirements for the regex are:
It should not contain hyphens AND
It should contain atleast 1 number
The expressions that I tried are:=
^(?!.*-)
This matches all non-hyphenated words but I am not able to figure out how to additionally add the second condition.
^(?!.*-(?=/d{1,}))
I tried using double lookahead but I am not sure about the syntax to use for it. This matches ID101 but also matches STACKOVERFLOW
Sample Words Which Should Match:
1DRIVE , ID100 , W1RELESS
Sample Words Which Should Not Match:
Basically any non-numeric string (like STACK , OVERFLOW) or any hyphenated words (Test-11 , 24-hours)
Additional Info:
I am using library re and compiling the regex patterns and using re.search for matching.
Any assistance would be very helpful as I am new to regex matching and am stuck on this for quite a few hours.
Maybe,
(?!.*-)(?=.*\d)^.+$
might simply work OK.
Test
import re
string = '''
abc
abc1-
abc1
abc-abc1
'''
expression = r'(?m)(?!.*-)(?=.*\d)^.+$'
print(re.findall(expression, string))
Output
['abc1']
If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.
RegEx Circuit
jex.im visualizes regular expressions:
RegEx 101 Explanation
/
(?!.*-)(?=.*\d)^.+$
/
gm
Negative Lookahead (?!.*-)
Assert that the Regex below does not match
.* matches any character (except for line terminators)
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
- matches the character - literally (case sensitive)
Positive Lookahead (?=.*\d)
Assert that the Regex below matches
.* matches any character (except for line terminators)
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\d matches a digit (equal to [0-9])
^ asserts position at start of a line
.+ matches any character (except for line terminators)
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of a line
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
I came up with -
^[^-]*\d[^-]*$
so we need at LEAST one digit (\d)
We need the rest of the string to contain anything BUT a - ([^-])
We can have unlimited number of those characters, so [^-]*
but putting them together like [^-]*\d would fail on aaa3- because the - comes after a valid match- lets make sure no dashes can sneak in before or after our match ^[-]*\d$
Unfortunately that means that aaa555D fails. So we actually need to add the first group again- ^[^-]*\d[^-]$ --- which says start - any number of chars that aren't dashes - a digit - any number of chars that aren't dashes - end
Depending on style, we could also do ^([^-]*\d)+$ since the order of the digits/numbers dont matter, we can have as many of those as we want.
However, finally... this is how I would ACTUALLY solve this particular problem, since regexes may be powerful, but they tend to make the code harder to understand...
if ("-" not in text) and re.search("\d", text):
Good morning,
I have a string that I need to parse and print the content of two named group knowing that one might not exist.
The string looks like this (basically content of /proc/pid/cmdline):
"""
<some chars with letters / numbers / space / punctuation> /CLASS_NAME:myapp.server.starter.StarterHome /PARAM_XX:value_XX /PARAM_XX:value_XX /CONFIG_FILE:myapp.server.config.myconfig.txt /PARAM_XX:value_XX /PARAM_XX:value_XX /PARAM_XX:value_XX <some chars with letters / numbers / space / punctuation>
"""
my processes have almost the same pattern, that is:
/CLASS_NAME:myapp.server.starter.StarterHome is always present, but
/CONFIG_FILE:myapp.server.config.myconfig.txt is NOT always present.
I'm using python2 with re module to catch the values. So far my pattern looks like this and I'm able to catch the value I want corresponding to /CLASS_NAME
re.compile('CLASS_NAME:\w+\W\w+\W\w+\W(?P<class>\w+)')
The because /CONFIG_FILE is present or not, I added the following to myregexp:
re.compile(r"""CLASS_NAME:\w+\W\w+\W\w+\W(?P<class>\w+).*?
(CONFIG_FILE:\w+\W\w+\W\w+\W(?P<cnf>\w+.txt))?
""", re.X)
My understanding is that the second part of my rexexp is optional because the whole part is between parenthesis followed by ?.
Unfortunately my assumption is wrong as it couldn't catch it
I also tried by removing the 1st ? but it didn't help.
I gave several tries through PYTHEX to try to understand my regexp but couldn't find a solution.
Could anyone have any suggestion to resolve my case?
You can wrap the whole optional part within an optional non-capturing group and make the capturing group for CONFIG_FILE obligatory:
re.compile(r"""CLASS_NAME:(?:\w+\W+){3}(?P<class>\w+)(?:.*?
(CONFIG_FILE:(?:\w+\W+){3}(?P<cnf>\w+\.txt)))?
""", re.X)
In case there are newlines, use re.X | re.S modifier options. Note that \w+\W\w+\W\w+\W is better written as (?:\w+\W+){3}.
See the regex demo
The main difference is (?:.*?(CONFIG_FILE:(?:\w+\W+){3}(?P<cnf>\w+\.txt)))? part:
(?: - start of an optional (as there is a greedy ? quantifier after it) non-capturing group matching
.*? - any 0+ chars, as few as possible
(CONFIG_FILE:(?:\w+\W+){3}(?P<cnf>\w+\.txt)) - matches
CONFIG_FILE: - a literal substring
(?:\w+\W+){3} - three sequences of 1+ word chars followed with 1+ non-word chars
(?P<cnf>\w+\.txt) - Group cnf: 1+ word chars, a dot (note it should be escaped) and then txt
)? - end of the optional non-capturing group (that will be tried once)