NSPredicate and Regexes
NSPredicate and Regexes
- Subject: NSPredicate and Regexes
- From: Romain Pechayre <email@hidden>
- Date: Sun, 30 Mar 2008 12:26:48 +0200
Hi All,
I am new to both cocoa and regex, so I would not be surprised to see
that I just did a silly mistake in the regex in the following code:
NSString* regexFormat=@"[+-]?([0-9]*\.?[0-9]+)?[A-Z|a-z][A-Z|a-z|
0-9]*([+-]?([0-9]*\.?[0-9]+)?[A-Z|a-z][A-Z|a-z|0-9]*)*";
NSString* equation =@"X1+2X2+3X3";
NSPredicate* regexTest=[NSPredicate predicateWithFormat:@"SELF MATCHES
%@",regexFormat];
if ([regexTest evaluateWithObject:equation] == YES) {
NSLog(@"Equation OK");
} else{
NSLog(@"Bad format for equation in Objective");
NSLog(equation);
}
I want to match any linear equation using the regex regexFormat. It
works in most cases ( ie, it matches what I want and does not match
what I don't), except that it does match X1+2X2++3X3, which is quite
worrying. In addition to this, it does not match neither X1+2X2++X3
nor X1 +2X2++3.1X3.
I have done all the manipulations that came to my mind to check it and
it looks like the presence of a integer ( and not floating)
coefficient in front of a variable which is not the first one in the
equation allows a double + in front of it. It also works with +- but
does not work with more than two +.
Finally, I have tried it in python ( see code below ), and it does
exactly what I want. Do you think there could be an issue with regexes
using NSPredicate ?
Does anyone have a clue ?
Best regards,
rpechayr
Here the "equivalent" code in python :
#!/usr/bin/env python
# encoding: utf-8
import sys
import os
import re
def main():
reg ='[+-]?([0-9]*\.?[0-9]+)?[A-Z|a-z][A-Z|a-z|0-9]*([+-]?([0-9]*\.?
[0-9]+)?[A-Z|a-z][A-Z|a-z|0-9]*)*'
prog=re.compile(reg)
result = prog.match('X1+2X2++1.00X3')
print result.group(0)
if __name__ == '__main__':
main()
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