[Tutor] finding special character string

[Marilyn Davis]

On Sun, June 1, 2008 10:30 am, Alan Gauld wrote:

> "Kent Johnson" <kent37 at tds.net> wrote
>
>
>> Assuming the strings are non-overlapping, i.e. the closing "." of
>> one string is not the opening "." of another, you can find them all with
>> import re re.findall(r'\..*?\.', text)
>
> Hmm, my regex hopelessness comes to the fore again.
> Why a *?
> I would probably have guessed the pattern to be
>
>
> \..+?\.
>
>
> What am I missing?

I think you're right.

Maybe the specification means there should be word boundaries?

r"\b\..+?\.\b"

This little program includes a function to test regular expressions.  I
find it helpful and I give it to students.  I think such programs exist on
the net.

#!/usr/bin/env python
"""This exercise is from the book "Perl by Example" by Ellie Quigley.
The exercise in Ellie's book asks us to print the city and state
where Norma lives.

I used this little program to develop the regular expression."""

import re
import sys

def ReTest(re_str, data, flags):
    """Test the re_str against the data with flags.

    If it doesn't find a hit, try again with one character trimmed off
    the end, and again, and again, until a hit is found.  Then give
    a report.
    """
    for i in range(len(re_str), 0, -1):
        try:
            m = re.search(re_str[:i], data, flags)
            m.groups() # generate an error
        except:
            continue
        else:
            print "This much worked:"
            print re_str[:i]
            print "It broke here:"
            print re_str[i:]
            break

def main():
    data = """Tommy Savage:408-724-0140:1222 Oxbow Court, Sunnyvale, CA
94087:5/19/66:34200
Lesle Kerstin:408-456-1234:4 Harvard Square, Boston, MA 02133:4/22/62:52600
JonDeLoach:408-253-3122:123 Park St., San Jose, CA 94086:7/25/53:85100
Ephram Hardy:293-259-5395:235 Carlton Lane, Joliet, IL 73858:8/12/20:56700
Betty Boop:245-836-2837:6937 Ware Road, Milton, PA 93756:9/21/46:43500
Wilhelm Kopf:846-836-2837:6937 Ware Road, Milton, PA 93756:9/21/46:43500
Norma Corder:397-857-2735:74 Pine Street, Dearborn, MI 23874:3/28/45:245700
James Ikeda:834-938-8376:23445 Aster Ave., Allentown, NJ 83745:12/1/38:45000
Lori Gortz:327-832-5728:3465 Mirlo Street, Peabody, MA 34756:10/2/76:35200
Barbara Kerz:385-573-8326:832 Pnce Drive, Gary, IN 83756:12/15/46:26850
"""
    re_str = r"""
    ^%s    # Line starts with the name
    \b     # followed by a non-word character
    (?:    # Un-captured group
    [^:]+? # of non-colons
    :){2}  # followed by a colon, twice
    x      # a mistake!!!
    \d+?   # some digits
    [ ]+   # one or spaces in []
    (?P<town># capturing a group
    # named town. This sequence cannot be
    # split for comments.
    [^:\d] # with no colons or digits
    +?)    # one or more times
    \d      # a digit ends the match
    """ % 'Norma'
    ReTest(re_str, data, re.VERBOSE + re.MULTILINE)

if __name__ == '__main__':
    main()
"""
$ ./re_test.py
This much worked:

    ^Norma    # Line starts with the name
    \b     # followed by a non-word character
    (?:    # Un-captured group
    [^:]+? # of non-colons
    :){2}  # followed by a colon, twice

It broke here:
x      # a mistake!!!
    \d+?   # some digits
    [ ]+   # one or spaces in []
    (?P<town># capturing a group
    # named town. This sequence cannot be
    # split for comments.
    [^:\d] # with no colons or digits
    +?)    # one or more times
    \d      # a digit ends the match
"""

Marilyn Davis


>
>
> Alan G.
>
>
>
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