Splitting list into sublists by given separator in python

Question

I'm trying to build n-grams which don't cross a period symbol. Split() only works for functions and list[index] only works with an index. Is there a way to access/split/divide a list by giving it a string/an element? Here is a snippet of my current function:

text = ["split","this","stuff",".","my","dear"]

def generate_ngram(rawlist, ngram_order):
        """
        Input: List of words or characters, ngram-order ["this", "is", "an", "example"], 2
        Output: Set of tuples or words or characters {("this", "is"),("is","an"),...}
        """

    list_of_tuples = []
    for i in range(0, len(rawlist) - ngram_order + 1):
        ngram_order_index = i + ngram_order    
        generated_ngram = rawlist[i : ngram_order_index]

        #if "." in generated_ngram:
            #generated_ngram . . . 

        generated_tuple = tuple(generated_ngram)  
        list_of_tuples.append(generated_tuple)

    return set(list_of_tuples)

generate_ngram(text,3)

currently returns:

{('.', 'my', 'dear'),
 ('stuff', '.', 'my'),
 ('split', 'this', 'stuff'),
 ('this', 'stuff', '.')}

but it should ideally return:

{('split', 'this', 'stuff'),
 ('this', 'stuff', '.')}

Any idea on how to achieve this? Thanks for your help!

Answer 1

I'm not sure if this is exactly what you need, but this function generates ngrams that can only contain stop words (in this case period) at the end:

STOPWORDS = {"."}

def generate_ngram(rawlist, ngram_order):
    # All ngrams
    ngrams = zip(*(rawlist[i:] for i in range(ngram_order)))
    # Generate only those ngrams that do not contain stop words before the end
    return (ngram for ngram in ngrams if not any(w in STOPWORDS for w in ngram[:-1]))

text = ["split", "this", "stuff", ".", "my", "dear"]
print(*generate_ngram(text, 3), sep="\n")
# ('split', 'this', 'stuff')
# ('this', 'stuff', '.')
print(*generate_ngram(text, 2), sep="\n")
# ('split', 'this')
# ('this', 'stuff')
# ('stuff', '.')
# ('my', 'dear')

Note this function returns a generator. You can convert it to a list wrapping it with list(...) if you want, or you can directly iterate over it.

EDIT: You may find the equivalent syntax below more readable.

def generate_ngram(rawlist, ngram_order):
    # Iterate over all ngrams
    for ngram in zip(*(rawlist[i:] for i in range(ngram_order))):
        # Yield only those not containing stop words before the end
        if not any(w in STOPWORDS for w in ngram[:-1]):
            yield ngram