Python

Recursive function

Please support our Python advertiser: Programming Forums - DaniWeb Sister Site

Thread Solved

•

Join Date: Mar 2007

Posts: 1

Reputation: cmpt is an unknown quantity at this point

Solved Threads: 0

cmpt

Offline

Newbie Poster

Recursive function

Mar 30th, 2007

search(l, key):

if len(l) == 0:
return False
elif l[0] == key:
return True
else:
return search(l[1:], key)

I was just wondering if there is any way that i can get rid of "elif" statement. The function is suppose to return False if the key is not in the list "l" and True if otherwise. (it has to be a recursive function though)

And plus...
How would I modify this function so that it returns the index of key in l instead of True? (it still returns False if key is not in l)

I am not very good with computer programming...please someone help me? It would be greatly appreciated. =)
Thanks!

Last edited by cmpt; Mar 30th, 2007 at 8:38 pm.

•

Join Date: Sep 2005

Posts: 133

Reputation: mawe is an unknown quantity at this point

Solved Threads: 58

mawe

Offline

Junior Poster

Re: Recursive function

Mar 31st, 2007

Hi!

The first one without any if-elif:

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
def search(l, key):
    return key in l
def search(l, key):
    return key in l

For the second one, .index() is your friend

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
def search(l, key):
    if key in l: return l.index(key)
    return False
def search(l, key):
    if key in l: return l.index(key)
    return False

EDIT: Oh sorry, I didn't see it had to be recursive.

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
def search(l, key, index=0):
    if l:
        if l[0] == key: return index
        return search(l[1:], key, index+1)
    return False
def search(l, key, index=0):
    if l:
        if l[0] == key: return index
        return search(l[1:], key, index+1)
    return False

Regards, mawe

Last edited by mawe; Mar 31st, 2007 at 12:21 am.

•

Join Date: Jul 2008

Posts: 12

Reputation: docaholic is an unknown quantity at this point

Solved Threads: 1

docaholic

Offline

Newbie Poster

Re: Recursive function

Mar 22nd, 2009

Is there anyway you can do the last code without adding the index=0 to the search function arguments?

•

Join Date: Jul 2008

Posts: 984

Reputation: Gribouillis is a jewel in the rough

Solved Threads: 222

Gribouillis Gribouillis is offline

Offline

Posting Shark

Re: Recursive function

Mar 23rd, 2009

Yes there is

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
def search(l, key):
    if l:
        if l[0] == key:
            return 0
        s = search(l[1:], key)
        if s is not False:
            return s + 1
    return False
def search(l, key):
    if l:
        if l[0] == key:
            return 0
        s = search(l[1:], key)
        if s is not False:
            return s + 1
    return False

However, the good way to do this is to use the builtin index function !

•

Join Date: Jul 2008

Posts: 12

Reputation: docaholic is an unknown quantity at this point

Solved Threads: 1

docaholic

Offline

Newbie Poster

Re: Recursive function

Mar 23rd, 2009

dumb question but...what does if l: do?

•

Join Date: May 2008

Posts: 950

Reputation: Paul Thompson has a spectacular aura about

Solved Threads: 147

Paul Thompson Paul Thompson is offline

Offline

previously paulthom12345

Re: Recursive function

Mar 23rd, 2009

It checks to see if l is existant, if there are no elelments in l then it will return False because your key cant be in an empty list! Therefore avoiding any unwanted Exceptions!

Make it idiot proof and someone will make a better idiot.
Check out my Site | and join us on IRC | Python Specific IRC

•

Join Date: Oct 2004

Posts: 4,146

Reputation: vegaseat is just really nice

Solved Threads: 949

vegaseat

Online

DaniWeb's Hypocrite

Re: Recursive function

Mar 23rd, 2009

BTW, the letter 'l' is a rather poor choice for a variable name, since it looks much like the number '1' on many editors. I have gotten in the habit to use 'mylist' or 'qq' for casual lists.

May 'the Google' be with you!