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Negative lookbehind - fail if you have just passed over [python]
Regular Expressions - Extra Elements example from a Well House Consultants training course
More on Regular Expressions - Extra Elements [link]

This example is described in the following article(s):
   • Python regular expressions - repeating, splitting, lookahead and lookbehind - [link]
   • Looking ahead and behind in Regular Expressions - double matching - [link]

Source code: lookbehind.py Module: Q803

import re

# word ensing "ing?on" but NOT is ss just before the "ing?on"
samevalues = re.compile (r'(\w+)(?<!ss)ing.on')

# Very odd extra example - don't allow leading space either!
# gives "rp" and "unt", then "Lav" and "unt"
# samevalues = re.compile (r'(?<!\s)(\w+)(?<!ss)ing.on')

info = ["Hello Orpington, Blessington, Huntingdon", \
        "Lavington, Blessington, Huntingdon"]

for demo in info:
        result = samevalues.findall(demo)
        if result:
                print demo, "YES"
                print result
        else:
                print demo, "NO"

"""

Hello Orpington, Blessington, Huntingdon YES
['Orp', 'Hunt']
Lavington, Blessington, Huntingdon YES
['Lav', 'Hunt']
wizard:pyoo graham$

"""

Learn about this subject
This module and example are covered on our public Regular Expressions course. If you have a group of three or more trainees who need to learn the subject, we can also arrange a private or on site course for you.

Books covering this topic
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Other Examples
This example comes from our "Regular Expressions - Extra Elements" training module. You'll find a description of the topic and some other closely related examples on the "Regular Expressions - Extra Elements" module index page.

Full description of the source code
The complete training module that describes this source code is availble for download (for limited use) from our download centre.

Other resources
• Our Solutions centre provides a number of longer technical articles.
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This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.

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