Programming Forums - Retaining the contents of a list during a recursive function

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- - Retaining the contents of a list during a recursive function (http://www.programmingforums.org/showthread.php?t=11912)

nytrokiss

Nov 16th, 2006 11:31 PM

Retaining the contents of a list during a recursive function

def find_all_items(site):

    site = urllib.urlopen(site).read()

    all_items = re.findall(r'watch\.asp\?\w+\=\w*\&\w*\=\w+',site)

    next_page = re.findall(r'Watches\.asp\?\w+\=[0-9]+\&pg\=\w+',site)

    try:

        find_all_items(urllib.basejoin("<some url>",next_page[0]))

    except IndexError:

        pass

    return remove_dups(all_items) # ,<---- this removes all the duplicate items

How do i keep the value of all_items that i have within the first function call and return a list of all the items at once also from the second function call

Now the list is being overwritten

DaWei

Nov 16th, 2006 11:34 PM

Is this a tutorial or a question? It doesn't seem to say, anywhere.

titaniumdecoy

Nov 17th, 2006 1:06 AM

It never fails to amaze me how so many of the newcomers to this forum have such unbelievably bad (written) communication skills.

Arevos

Nov 17th, 2006 2:34 AM

def find_all_items(site):

    site = urllib.urlopen(site).read()

    all_items = re.findall(r'watch\.asp\?\w+\=\w*\&\w*\=\w+',site)

    next_page = re.findall(r'Watches\.asp\?\w+\=[0-9]+\&pg\=\w+',site)

    try:

        all_items.extend(find_all_items(urllib.basejoin("<some url>",next_page[0])))

    except IndexError:

        pass

    return remove_dups(all_items) # ,<---- this removes all the duplicate items

Also, you may want to think about using the set() data type, which contains only unique values and doesn't retain order.

Perhaps:

def find_all_items(site):

    site = urllib.urlopen(site).read()

    all_items = set(re.findall(r'watch\.asp\?\w+\=\w*\&\w*\=\w+',site))

    next_page = re.findall(r'Watches\.asp\?\w+\=[0-9]+\&pg\=\w+',site)

    try:

        all_items.union(find_all_items(urllib.basejoin("<some url>",next_page[0])))

    except IndexError:

        pass

    return all_items

And I can't see a Python HTML parsing problem without mentioning Beautiful Soup. Though your problem might be simple enough that it needs only regexs.

nytrokiss

Nov 17th, 2006 3:01 AM

I tried both the examples the issue is that the list all_items is cleared when the function is called again!

Arevos

Nov 17th, 2006 3:20 AM

Hm. It might help if you showed all your code, as it's difficult to understand exactly what you're asking for. Do you want some sort of persistence? Then you either need a functor:

class FindAllItemsFunctor
    def __init__(self):
        self.all_items = []
    def __call__(self, site):
        # Your find_all_items code using self.all_items instead of all_items
 
find_all_items = FindAllItemsFunctor()

Or you need to use some functions within functions:

def find_all_items_creater():
    all_items = []
    def find_all_items(site):
        # ...
    return find_all_items
 
find_all_items = find_all_items_creater()

Or you could use a global variable:

all_items = []
def find_all_items(site):
    global all_items
    # ...

Or even do something clever with the function's parameters:

def find_all_items(site, all_items = [])
    # ...

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