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Regex python help for coordinate format

I'm working on a program that takes the input in a particular format:
example "(1,2)(2,3)(4,3)". They are coordinates and there can be infinitely many coordinates "(1,2)(2,3)(4,3)...(a,b)". I'm writing a function "checkFormat(str)" that returns true if the format is satisfied. I've tried writing a function without the use of regex but it proved too difficult. Need help with the regex expression.

Use ^ and $ to match the whole input. in between is one or more set of (...) filled with digits.
Assuming coordinates are integer and no extra space in between:
^((\((\d)+\,(\d)+)\))+$
if +/- is allowed and 0 has no sign and could not be extended (00 or 01 not accepted)
^(\(([-\+]?[1-9]\d*|0)\,(([-\+]?[1-9]\d*)|0)\))+$
If decimal numbers are included:
^(\(([-\+]?[1-9]\d*|0)([.]\d+)?\,(([-\+]?[1-9]\d*)|0)([.]\d+)?\))+$
To check if the input match or not:
import re
pattern=r'^(\(([-\+]?[1-9]\d*|0)([.]\d+)?\,(([-\+]?[1-9]\d*)|0)([.]\d+)?\))+$'
input='(0,2)(1,2)'
result=bool(re.match(pattern,input))

Finding the end of a contiguous substring of a string without iteration or RegEx

I'm trying to write an iterative LL(k) parser, and I've gotten strings down pretty well, because they have a start and end token, and so you can just "".join(tokenlist[string_start:string_end]).
Numbers, however, do not, and only consist of .0123456789. They can occur at any given point in a program, have any arbitrary length and are delimited purely by non-numerals.
Some examples, because that definition is pretty vague:
56 123.45/! is 56 and 123.45 followed by two other tokens
565.5345.345 % is 565.5345, 0.345 and two other tokens (incl. whitespace)
The problem I'm trying to solve is how the parser should figure out where a numeric literal ends. (Note that this is a context-free, self-modifying interpretive grammar thus there is no separate lexical analysis to be done.)
I could and have solved this with iteration:
def _next_notinst(self, atindex, subs = DIGITS):
"""return the next index of a char not in subs"""
for i, e in enumerate(self.toklist[atindex:]):
if e not in subs:
return i - len(self.toklist)
else:
break
return self.idx.v
(I don't think I need to clarify the variables, since it's an example and extremely straightforward.)
Great! That works, but there are at least two issues:
It's O(n) for a number with digit-length n. Not ideal.*
The parser class of which this method is a member is already using a while True: to cycle over arbitrary parts of the string, and I would prefer not having remotely nested loops when I don't need to.
From the previous bullet: since the parser uses arbitrary k lookahead and skipahead, parsing each individual token is absolutely not what I want.
I don't want to use RegEx mostly because I don't know it, and using it for this right now would make my code uncomprehendable to me, its creator.
There must be a simple, < O(n) solution to this, that simply collects the contiguous numerals in a string given a starting point, up until a non-numeral.
*Yes, I'm fully aware the parser itself is O(n), but we don't also need the number catenator to be > O(n). If you don't believe me, the string catenator is O(1) because it simply looks for the next unescaped " in the program and then joins all the chars up to that. Can't I do the same thing for numbers?

My other answer was actually erroneous due to lack of testing.
I decided to suck it up and learn a little bit of RegEx just because it's the only other way to solve this.
^([.\d]+[.\d]+|[.\d]) works for what I want, and matches these:
123.43.453""
.234234!/%
but not, for example:
"1233

regex does not match only upper case letters, despite being instructed to do so

I'm making a script to crawl through a web page and find all upper case names, equalling a number (ex. DUP_NB_FUNC=8). The part where my regular expression has to match only upper case letters however, does not seem to be working properly.
value = re.findall(r"[A-Z0-9_]*(?==\d).{2,}", input)
|tc_apb_conf_00.v:-:DUP_NB_FUNC=2
|:-:DUP_NB_FUNC=2
|:-:DUP_NB_FUNC=4
|:-:DUP_NB_FUNC=5
|tc_apb_conf_01.v:-:DUP_NB_FUNC=8
Desired output should look something like the above. However, I am getting:
|tc_apb_conf_00.v:-:=1" name="viewport"/>
|:-:DUP_NB_FUNC=2
|:-:DUP_NB_FUNC=4
|:-:DUP_NB_FUNC=5
|tc_apb_conf_01.v:-:DUP_NB_FUNC=8
Based on the input I can see its finding a match starting at =1. I don't however understand why as I've put only A-Z in the regex range. I'd really appreciate a bit of assistance and clearing up.

This should be help:
[A-Z0-9_]+(?==\d).{2,}
or
\b[A-Z0-9_]*(?==\d).{2,}\b
But anyway your regex quite weird, according to your requirement above I suggest this
[A-Z0-9_]+=\d+
Instead of using
(?==\d).{2,}: any letters two or more and make sure that the first two letter are = and a one integer respectively,
you can just use
=\d+

Try this.
value = re.findall(r"[A-Z0-9_]+(?==\d).{2,}", input)
You want the case sensitive match to match at least once, which means you want the + quantifier, not the * quantifier, that matches between zero and unlimited times.

I will suggest you define your pattern and check you input if it is available
for i in tlist:
value=re.compile(r"[A-Z0-9_:-.]+=\d+")
jee=value.match(i)
if jee is not None:
print i
tlist contains your input

Regex named conditional lookahead (in Python)

I'm hoping to match the beginning of a string differently based on whether a certain block of characters is present later in the string. A very simplified version of this is:
re.search("""^(?(pie)a|b)c.*(?P<pie>asda)$""", 'acaaasda')
Where, if <pie> is matched, I want to see a at the beginning of the string, and if it isn't then I'd rather see b.
I'd use normal numerical lookahead but there's no guarantee how many groups will or won't be matched between these two.
I'm currently getting error: unknown group name. The sinking feeling in my gut tells me that this is because what I want is impossible (look-ahead to named groups isn't exactly a feature of a regular language parser), but I really really really want this to work -- the alternative is scrapping 4 or 5 hours' worth of regex writing and redoing it all tomorrow as a recursive descent parser or something.
Thanks in advance for any help.

Unfortunately, I don't think there is a way to do what you want to do with named groups. If you don't mind duplication too much, you could duplicate the shared conditions and OR the expressions together:
^(ac.*asda|bc.*)$
If it is a complicated expression you could always use string formatting to share it (rather than copy-pasting the shared part):
common_regex = "c.*"
final_regex = "^(a{common}asda|b{common})$".format(common=common_regex)

You can use something like that:
^(?:a(?=c.*(?P<pie>asda)$)|b)c.*$
or without .*$ if you don't need it.

Regular expression how to get middle strings

I want to search for string that occurs between a certain string. For example,
\start
\problem{number}
\subproblem{number}
/* strings that I want to get */
\subproblem{number}
/* strings that I want to get */
\problem{number}
\subproblem{number}
...
...
\end
More specifically, I want to get problem number and subproblem number and strings between which is answer.
I somewhat came up with expression like
'(\\problem{(.*?)}\n)? \\subproblem{(.*?)} (.*?) (\\problem|\\subproblem|\\end)'
but it seems like it doesn't work as I expect. What is wrong with this expression?

This one:
(?:\\problem\{(.*?)\}\n)?\\subproblem\{(.*?)\}\n+(.*?)\n+(?=\\problem|\\subproblem|\\end)
returns three matches for me:
Match 1:
group 1: "number"
group 2: "number"
group 3: "/* strings that I want to get */"
Match 2:
group 1: null
group 2: "number"
group 3: "/* strings that I want to get */"
Match 3:
group 1: "number"
group 2: "number"
group 3: " ...\n ..."
However I'd rather parse it in two steps.
First find the problem's number (group 1) and content (group 2) using:
\\problem\{(.*?)\}\n(.+?)\\end
Then find the subproblem's numbers (group 1) and contents (group 2) inside that content using:
\\subproblem\{(.*?)\}\n+(.*?)\n+(?=\\problem|\\subproblem|\\end)

TeX is pretty complicated and I'm not sure how I feel about parsing it using regular expressions.
That said, your regular expression has two issues:
You're using a space character where you should just consume all whitespace
You need to use a lookahead assertion for your final group so that it doesn't get eaten up (because you need to match it at the beginning of the regex the next time around)
Give this a try:
>>> v
'\\start\n\n\\problem{number}\n\\subproblem{number}\n\n/* strings that I want to get */\n\n\\subproblem{number}\n\n/* strings that I want to get */\n\n\\problem{number}\n\\subproblem{number}\n ...\n ...\n\\end\n'
>>> re.findall(r'(?:\\problem{(.*?)})?\s*\\subproblem{(.*?)}\s*(.*?)\s*(?=\\problem{|\\subproblem{|\\end)', v, re.DOTALL)
[('number', 'number', '/* strings that I want to get */'), ('', 'number', '/* strings that I want to get */'), ('number', 'number', '...\n ...')]

If the question really is "What is wrong with this expression?", here's the answer:
You're trying to match newlines with a .*?. You need (?s) for that to work.
You have explicit spaces and newlines in the middle of the regex that don't have any corresponding characters in the source text. You need (?x) for that to work.
That may not be all that's wrong with the expression. But just adding (?sx), turning it into a raw string (because I don't trust myself to mix Python quoting and regex quoting properly), and removing the \n gives me this:
r'(?sx)(\\problem{(.*?)}? \\subproblem{(.*?)} (.*?)) (\\problem|\\subproblem|\\end)'
That returns 2 matches instead of 0, and it's probably the smallest change to your regex that works.
However, if the question is "How can I parse this?", rather than "What's wrong with my existing attempt?", I think impl's solution makes more sense (and I also agree with the point about using regex to parse TeX being usually a bad idea)—-or, even better, doing it in two steps as Regexident does.
if using regex to parse TeX is not good idea, then what method would you suggest to parse TeX?
First of all, as a general rule of thumb, if I can't write the regex to solve a problem by myself, I don't want to solve it with a regex, because I'll have a hard time figuring it out a few months from now. Sometimes I break it down into subexpressions, or use (?x) and load it up with comments, but usually I look for another way.
More importantly, if you have a real parser that can consume your language and give you a tree (or whatever's appropriate) that you can walk and search—as with, e.g. etree for XML—then you've got 90% of a solution for every problem you're going to come up with in dealing with that language. A quick&dirty regex (especially one you can't write on your own) only gets you 10% of the way to solving the next problem. And more often than not, if I've got a problem today, I'm going to have more of them in the next few months.
So, what's a good parser for TeX in Python? Honestly, I don't know. I know scipy/matplotlib has something that does it, so I'd probably look there first. Beyond that, check Google, PyPI, and maybe tex.stackexchange.com. The first things that turn up in a search are Texcaller and plasTeX. I have no idea how good they are, or if they're appropriate for your use case, but it shouldn't take long to skim the tutorials and find out.
If it turns out that there's nothing out there, and it comes down to writing something myself with, e.g., pyparsing vs. regexes, then it's a tougher choice. Some languages, it's very easy to define just the subset you care about and leave the rest as giant uninterpreted tokens, in which case a real parser will be just as easy as a regex, so you might as well go that way. Other languages, you have to handle half the syntax before you can do anything useful, so I wouldn't even try. I'd have to put a bit of time into thinking about it and experimenting both ways before deciding which way to go.