How to decrement a list index in a loop

Question

In my code below I am taking the split_message list and querying an API. If there are no results, my next step would be to decrement the index of the list by -1, so I remove the last item from the list and retry the search. If there are no results again, I would like to repeat the process until I receive results.

---

import requests
import json

message = "if i can\'t let it go out of my mind"

split_message = message.split()

length = len(split_message)

def decrementList():
    initial_request = requests.get('http://ws.spotify.com/search/1/track.json?q='+"%20"
                                   .join(split_message[:]))
    json_string = initial_request.content
    json_dict = json.loads(json_string)
    num_results = json_dict['info']['num_results']
    if num_results == 0:
        print "Sorry, no match!"
    if num_results > 0:
        print "Result found!"

decrementList()

Effectively, my next step would be to take this:

requests.get('http://ws.spotify.com/search/1/track.json?q='+"%20"
                                       .join(split_message[:]))

and turn it into this:

requests.get('http://ws.spotify.com/search/1/track.json?q='+"%20"
                                       .join(split_message[:-1]))

and then this:

requests.get('http://ws.spotify.com/search/1/track.json?q='+"%20"
                                       .join(split_message[:-2]))

And repeating until I get a match.

I can think of extremely non-pythonic ways to do this, but it seems like way too many if statements. So what would be the best and most pythonic solution to what I am trying to accomplish?

Answer 1

EDIT

Actually, I like this version more. A bit cleaner IMHO.

def decrementList(words):
    words_remaining = words[:]
    while words_remaining:
        url = 'http://ws.spotify.com/search/1/track.json?q='
        request = requests.get(url + '%20'.join(words_remaining))

        json_dict = json.loads(request.content)
        if json_dict['info']['num_results'] > 0:
            num_words_taken = len(words) - len(words_remaining)
            return num_words_taken, json_dict

        words_remaining.pop()

Got the list.pop inspiration from @falsetru, see other answer.

ORIGINAL ANSWER

Maybe this is more to your liking:

import requests
import json

message = "if i can\'t let it go out of my mind"

split_message = message.split()

def decrementList(words):
    for w in [words] + [words[:-x] for x in range(1,len(words))]:
        url = 'http://ws.spotify.com/search/1/track.json?q='
        request = requests.get(url + "%20".join(w))

        json_dict = json.loads(request.content)
        num_results = json_dict['info']['num_results']
        if num_results > 0:
            num_removed = len(words) - len(w)
            return num_removed, json_dict

num_words_removed, json_dict = decrementList(split_message)

The key is [words] + [words[:-x] for x in range(1,len(words))]. Assuming words = message.split(), you get the list

[
    ['if', 'i', 'can', 'let', 'it', 'go', 'out', 'of', 'my', 'mind'],
    ['if', 'i', 'can', 'let', 'it', 'go', 'out', 'of', 'my'],
    ['if', 'i', 'can', 'let', 'it', 'go', 'out', 'of'],
    ['if', 'i', 'can', 'let', 'it', 'go', 'out'],
    ['if', 'i', 'can', 'let', 'it', 'go'],
    ['if', 'i', 'can', 'let', 'it'],
    ['if', 'i', 'can', 'let'],
    ['if', 'i', 'can'],
    ['if', 'i'],
    ['if']
]

Which I believe does what you want, and it's arguably 'Pythonic'. The function will break out of the loop as soon as you get the results you want. It returns both the number of words you had to remove from the list to get some results, as well as the JSON dict resulting from the request.

Answer 2

Use list.pop:

>>> message = "if i can\'t let it go out of my mind"
>>> split_message = message.split()
>>> split_message.pop()
'mind'
>>> split_message
['if', 'i', "can't", 'let', 'it', 'go', 'out', 'of', 'my']
>>> split_message.pop()
'my'
>>> split_message
['if', 'i', "can't", 'let', 'it', 'go', 'out', 'of']