|  | How can we get to the end of a quote inside a string | | |
| | | Guest |  |
|  Posted: Sun Aug 31, 2008 2:29 pm Post subject: How can we get to the end of a quote inside a string |  |
Hi all,
Suppose I have a string which contains quotes inside quotes -
single and double quotes interchangeably -
s = "a1' b1 " c1' d1 ' c2" b2 'a2"
I need to start at b1 and end at b2 - i.e. I have to parse the
single quote strings from inside s.
Is there an existing string quote parser which I can use or
should I write a parser myself?
If somebody could help me on this I would be much obliged.
Regards
kR/\/ |
| |
| | | Wojtek Walczak | |
| | Posted: Sun Aug 31, 2008 5:20 pm Post subject: Re: How can we get to the end of a quote inside a string | |
On Sun, 31 Aug 2008 07:29:26 -0700 (PDT), rajmohan.h@gmail.com wrote:
| Quote: | Suppose I have a string which contains quotes inside quotes -
single and double quotes interchangeably -
s = "a1' b1 " c1' d1 ' c2" b2 'a2"
s = "a1' b1 " c1' d1 ' c2" b2 'a2"
File "<stdin>", line 1 |
s = "a1' b1 " c1' d1 ' c2" b2 'a2"
^
SyntaxError: invalid syntax
Writing a small parser for your needs shouldn't be that hard.
To some extent you can use regular expressions:
| Quote: | re.findall(re.compile("\".*?\""), s)
['" c1\' d1 \' c2"']
re.findall(re.compile("\'.*?\'"), s)
['\' b1 " c1\'', '\' c2" b2 \'']
|
but it won't work in all cases. You can read more here:
LINK
--
Regards,
Wojtek Walczak,
LINK |
| |
| | | Antoon Pardon | |
| | Posted: Tue Sep 02, 2008 11:54 am Post subject: Re: How can we get to the end of a quote inside a string | |
On 2008-08-31, rajmohan.h@gmail.com <rajmohan.h@gmail.com> wrote:
| Quote: | Hi all,
Suppose I have a string which contains quotes inside quotes -
single and double quotes interchangeably -
s = "a1' b1 " c1' d1 ' c2" b2 'a2"
I need to start at b1 and end at b2 - i.e. I have to parse the
single quote strings from inside s.
Is there an existing string quote parser which I can use or
should I write a parser myself?
If somebody could help me on this I would be much obliged.
|
You could use a combination of split and join in this case.
#use a single quote as a seperator to split the string is a list of substrings
ls = s.split("'")
#remove what comes before the first and after the last single quote
ls = ls[1:-1]
#reassemble the string between the outermost single quotes.
s = "'".join(ls)
#strip spaces in front and after if you wish
s = s.strip()
--
Antoon Pardon |
| |
| | | Paul McGuire | |
| | Posted: Tue Sep 02, 2008 2:51 pm Post subject: Re: How can we get to the end of a quote inside a string | |
| |  | |
On Aug 31, 9:29 am, rajmoha...@gmail.com wrote:
| Quote: | Hi all,
Suppose I have a string which contains quotes inside quotes -
single and double quotes interchangeably -
s = "a1' b1 " c1' d1 ' c2" b2 'a2"
I need to start at b1 and end at b2 - i.e. I have to parse the
single quote strings from inside s.
|
Pyparsing defines a helper method called nestedExpr - typically it is
used to find nesting of ()'s, or []'s, etc., but I was interested to
see if I could use nestedExpr to match nested ()'s, []'s, AND {}'s all
in the same string (like we used to do in our algebra class to show
nesting of higher levels than parens - something like "{[a + 3*(b-c)]
+ 7}" - that is, ()'s nest within []'s, and []'s nest within {}'s).
This IS possible, but it uses some advanced pyparsing methods. I
adapted this example to map to your case - this was much simpler, as
""s nest within ''s, and ''s nest within ""s. I still keep a stack of
previous nesting, but I'm not sure this was absolutely necessary.
Here is the working code with your example:
from pyparsing import Forward, oneOf, NoMatch, Literal, CharsNotIn,
nestedExpr
# define special subclass of Forward, that saves previous contained
# expressions in a stack
class ForwardStack(Forward):
def __init__(self):
super(ForwardStack,self).__init__()
self.exprStack = []
self << NoMatch()
def __lshift__(self,expr):
self.exprStack.append(self.expr)
super(ForwardStack,self).__lshift__(expr)
return self
def pop(self):
self.expr = self.exprStack.pop()
# define the grammar
opening = ForwardStack()
closing = ForwardStack()
opening << oneOf(["'", '"'])
closing << NoMatch()
matchedNesting = nestedExpr(opening, closing, CharsNotIn('\'"'),
ignoreExpr=None)
# define parse-time callbacks
alternate = {'"':"'", "'":'"'}
def pushAlternate(t):
# closing expression should match the current opening quote char
closing << Literal( t[0] )
# if we find the other opening quote char, it is the beginning of
# a nested quote
opening << Literal( alternate[ t[0] ] )
def popClosing():
closing.pop()
opening.pop()
# when these expressions match, the parse action will be called
opening.setParseAction(pushAlternate)
closing.setParseAction(popClosing)
# parse the test string
s = """ "a1' b1 " c1' d1 ' c2" b2 'a2" """
print matchedNesting.parseString(s)[0]
Prints:
['a1', [' b1 ', [' c1', [' d1 '], ' c2'], ' b2 '], 'a2']
-- Paul |
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