Finding the regex for ///?

Question

This was posted to me

<*@google.com> wrote:

Hi Niklas, If you just want to map this: /region/city/category/ supposing its only this valid characters: [a-zA-Z0-9_] you can do the following: - main.py

application = webapp.WSGIApplication([('/([-\w]+)/([-\w]+)/([-\w]+)', handler)],debug=True)

and on your handler: class Handler(webapp.RequestHandler): def get(self, region, city, category): # Use those variables on the method Hope this helps!

My webapp is suppossed to handle URI like <region>/<city>/<category> with optional city and category e.g.

/rio_de_janeiro/grande_rio_de_janeiro/casas? #<region>/<city>/<category>
/gujarat/ahmedabad/vehicles-for_sale #<region>/<city>/<category>
/rio_de_janeiro/grande_rio_de_janeiro/ #<region>/<city>
/delhi #<region>

Etc Now I want to enable a request handler that can take optional arguments divided by the separator /. If I use the regex '/(.*) and variables in the request handler the first varible becomes a/b and the second variable becomes b so that is nearly what I want but a and b as 2 different variables instead. The regex I tried for the request handler is

application = webapp.WSGIApplication([('/(.*)',MyPage),

And the function head of my request handler is

class MyPage(RequestHandler):
    def get(self, location='frankfurt', category='electronics'):

To enable an HTTP query e.g. /frankfurt, /frankfurt/, /frankfurt/electronics, /madrid/apartments, /newyork, etc allowing all possible combinations. Can you advice me a regex that can achieve what I want? I want functionality like a mod_rewrite but for GAE.

Thanks

Clarification

It's just a question of "make the directory a variable" so to clarify here are some examples how it should behave

'/frankfurt', - put 'frankfurt' in variable 1 '/frankfurt/', - put 'frankfurt' in variable 1 '/frankfurt/electronics', - put 'frankfurt' in variable 1 and 'electronics' in virable 2 '/frankfurt/electronics/', same as above '/eu/frankfurt/electronics', same as above i.e. only last 2 groups count '/eu/frankfurt/electronics/', same as above 'toronto/lightnings', doesn't start with / so shan't work 'toronto/lightnings/', as above 'lima/cars/old', as above 'lima/cars/old/' as above

Typical cases I want to handle is /region/city/category i.e. if I apply the example to Brazil it could be /rio_de_janeiro/grande_rio_de_janeiro/casas? for /region/city/category or for India it could be /delhi/delhi/for_sale or /gujarat/ahmedabad/vehicles-for_sale

Solution

As far as I can tell the solution from the answer works for my purposes:

/(?:[^/]+)/?([^/]*)/?([^/]*)

Answer 1

After you have given more details, I can now propose another regex pattern:

import re

reg = re.compile('(?:/[^/]+(?=/[^/]+/[^/]+/?\Z)' # this partial RE matches the
                                                 # first of 3 groups, if 3
                 '|'    # OR
                 ')'   # nothing is catched
                 '/([^/]+)'  # the group always catching something
                 '(?:/([^/]+)?)?'  # the possible second or third group
                 '/?\Z' ) # the end

for ss in ('/frankfurt', '/frankfurt/',
           '/frankfurt/electronics', '/frankfurt/electronics/',
           '/eu/frankfurt/electronics', '/eu/frankfurt/electronics/',
           'toronto/lightnings', 'toronto/lightnings/',
           'lima/cars/old', 'lima/cars/old/',
           '/rio_de_janeiro/grande_rio_de_janeiro/casas/Magdalena'):
    mat = reg.match(ss)
    print ss,'\n',mat.groups() if mat else '- No matching -','\n'

result

/frankfurt 
('frankfurt', '') 
/frankfurt/ 
('frankfurt', '') 
/frankfurt/electronics 
('frankfurt', 'electronics') 
/eu/frankfurt/electronics/ 
('frankfurt', 'electronics') 
toronto/lightnings 
- No matching - 
lima/cars/old/ 
- No matching -
/rio_de_janeiro/grande_rio_de_janeiro/casas/Magdalena 
- No matching -

But, you know, using a regex isn't absolutely necessary to solve your problem:

for ss in ('/frankfurt', '/frankfurt/',
           '/frankfurt/electronics', '/frankfurt/electronics/',
           '/eu/frankfurt/electronics', '/eu/frankfurt/electronics/',
           'toronto/lightnings', 'toronto/lightnings/',
           'lima/cars/old', 'lima/cars/old/',
           '/rio_de_janeiro/grande_rio_de_janeiro/casas/Magdalena'):
    if ss[0]=='/':
        splitted = ss.rstrip('/').split('/')
        if len(splitted)==2:
            grps = splitted[::-1]
        elif len(splitted) in (3,4):
            grps = splitted[-2:]
        else:
            grps = None
    else:
        grps = None
    print ss,'\n',grps if grps else '- Incorrect string -','\n'

The results are the same as above.

Answer 2

You can try

/(?:[^/]+)/?([^/]*)/?([^/]*)

which will put 'a/b' in variable 1, 'a' in variable 2 and 'b' in variable 3. Not sure if that is what you want.

Answer 3

A solution that may work for you, though you may find it too hardcoded:

Routes for your app structured like this:

routes = [
    ('/foo/([a-zA-Z]+)/?', TestHandler),
    ('/foo/([a-zA-Z]+)/([a-zA-Z]+)/?', TestHandler),
    ('/foo/([a-zA-Z]+)/([a-zA-Z]+)/([a-zA-Z]+)/?', TestHandler)
]

And in your handler you'd check len(args), something like:

class TestHandler(webapp.RequestHandler):
    def get(self, *args):
        if len(args): # assign defaults, perhaps?

Answer 4

If you just want to map this: (region)/(city)/(category)/ supposing its only this valid characters: [a-zA-Z0-9_]

you can do the following: - main.py

application = webapp.WSGIApplication([
                    ('/([-\w]+)/([-\w]+)/([-\w]+)', Handler)
],debug=True)

and on your handler:

class Handler(webapp.RequestHandler):
    def get(self, region, city, category):
        # Use those variables on the method

Hope this helps!