Python Regex Problems

Question

I am having trouble converting a RegEx expression to python. I know that '(\\d+)' is the expression for a single integer, but I cannot figure out how to get an integer that is [2-9].

The RegEx expression is as follows:

[2-9][p-z][a-h][2-9][a-z]*[p-z][2-9][p-z][2-9][p-z]

This is my current expression but it produces many false positives as it is not specific enough:

          re1='(\\d+)'    # Integer Number 1
            re2='([a-z])'   # Any Single Word Character (Not Whitespace) 1
            re3='([a-z])'   # Any Single Word Character (Not Whitespace) 2
            re4='(\\d+)'    # Integer Number 2
            re5='((?:[a-z][a-z]+))' # Word 1
            re6='(\\d+)'    # Integer Number 3
            re7='([a-z])'   # Any Single Word Character (Not Whitespace) 3
            re8='(.)'   # Any Single Character 1
            re9='([a-z])'   # Any Single Word Character (Not Whitespace) 4

            ## Regex search for passcodes ## Thanks to Pierluigi Failla
            rg = re.compile(re1+re2+re3+re4+re5+re6+re7+re8+re9,re.IGNORECASE|re.DOTALL)
            m = rg.search(txt)
            if m:
                int1=m.group(1)
                w1=m.group(2)
                w2=m.group(3)
                int2=m.group(4)
                word1=m.group(5)
                int3=m.group(6)
                w3=m.group(7)
                c1=m.group(8)
                w4=m.group(9)
                txt2='"'+int1+w1+w2+int2+word1+int3+w3+c1+w4+'"'
                return [txt2]

But [2-9] is correct for matching an integer that is 2-9. So what do you want to match in the first place? What are false positives you are getting? What are examples of strings you are matching against? — crackmigg
– crackmigg, Commented May 20, 2013 at 17:08
This question is very unclear. The first expr and the code below do not match. — dansalmo
– dansalmo, Commented May 20, 2013 at 17:09
You want to use r'' raw strings to avoid all the doubled \`, and there is a re.VERBOSE` mode to make writing readable expressions easer than concatenating 9 separate strings.. — Martijn Pieters
– Martijn Pieters, Commented May 20, 2013 at 17:13
May be worth taking a read of this developers.google.com/edu/python/regular-expressions — rcbevans
– rcbevans, Commented May 20, 2013 at 17:16
\d+ isn't the pattern for one digit, it is for "one or a succession of digits" — eyquem
– eyquem, Commented May 20, 2013 at 17:18

Ian Knight · Accepted Answer · 2013-05-20 17:17:13Z

2

You should be able to use the range 2-9 in Python, like so: re1 = re.compile(r'[2-9]'). A test in my console then showed that re1.match('7') returns a MatchObject as you want, whereas re1.match('0') returns None, also as you want.

You also appear to have used the range [a-z] in re2, where you said you wanted [p-z] - similar issues in the other character ranges.

answered May 20, 2013 at 17:17

Ian Knight

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Mondrianaire Over a year ago

Thanks, I was aware that the expression I was using was a lot more lenient that I wanted to be, I was unsure if using [2-9] was correct syntax for python.

eyquem · Accepted Answer · 2013-05-21 01:11:53Z

1

I propose this code, based on what I see in your question:

import re

pat = ('([2-9])'        # Integer Number 1
       '([p-z])'        # Any Single Word Character (Not Whitespace) 1
       '([a-h])'        # Any Single Word Character (Not Whitespace) 2
       '([2-9])'        # Integer Number 2
       '([a-z]*[p-z]+)' # Word 1
       '([2-9])'        # Integer Number 3
       '([p-z])'        # Any Single Word Character (Not Whitespace) 3
       '(.)'            # Any Single Character 1
       '([p-z])'        # Any Single Word Character (Not Whitespace) 4
       )
rg = re.compile(pat)

txt = 'jiji4pa6fmlgkfmoaz8p#q,,,,,,,,,,'
m = rg.search(txt)
if m:
    text2 = "%s%s%s%s%s%s%s%s%s" % m.groups()
    print text2

# prints 4pa6fmlgkfmoaz8p#q

EDIT

text2 = ''.join(m.groups())  # is better

edited May 21, 2013 at 1:11

answered May 20, 2013 at 18:11

eyquem

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3 Comments

Mondrianaire Over a year ago

Based on other comments the \d is still matching every integer. Would't it be more specific to use ([2-9]) instead?

eyquem Over a year ago

Oh I'm really sorry. I copied from the series of re1,re2,etc but you're right: if you doesn't want digits 0 and 1, you must use [2-9] instead of \d. I corrected my code

eyquem Over a year ago

@Mondrianaire Thank you. I doesn't know where was my brain today; I edited my answer to give a simpler way to obtain the result in the case of this problem.

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