在循环期间从列表列表中删除元素

Question

I have a data structure info (a list of lists?) that I am constructing as follows:

pages     = [12, 41, 50, 111, 1021, 121]
bookCodes = ['M', 'P', 'A', 'C', 'A', 'M']
sentences = ['THISISASENTENCE',
             'ANDHEREISONEMOREEXAMP',
             'ALLFROMDIFFERENTBOOKS',
             'ANDFROMDIFFERENTPAGES',
             'MOSLTYTHESAMELENGTHS',
             'THISISSHORT'
             ]
info = list(zip(bookCodes, pages, sentences))

I am then iterating over this list (of zipped lists) on letter at a time. As some sentences are shorter than others (eg THISISSHORT ) I reach the final element before other sentences. In this case I want mask this element from future iterations completely but I don't want to filter it before I start my loop .

import random

letters_read = 0

for i in range(21):
    random.shuffle(info)
    for b, p, s in info:
        if len(s) <= i+1:
            print("End of sentence reached at position %s. Sentence: %s" % (i, s))
            continue    
        letters_read += 1

I am currently using continue to skip over elements where this is the case, and print a message to indicate the sentence that has reach its end. However, this will continue iterating over this element until the end of the loop. I want to exclude such elements from further iterations.

I have ~ 10,000 sentences in my list, and these can be as large as 2000 characters, so I am assuming that by masking such sentences from future iterations rather than skipping will increase the efficiency of my script.

Is it possible to remove/mask an element from this data structure during iteration? I've tried using info.remove(i) and del info[i] , but this doesn't work (seeing as this is not a list).

---

Output :

End of sentence reached at position 10. Sentence: THISISSHORT
End of sentence reached at position 11. Sentence: THISISSHORT
End of sentence reached at position 12. Sentence: THISISSHORT
End of sentence reached at position 13. Sentence: THISISSHORT
End of sentence reached at position 14. Sentence: THISISASENTENCE
End of sentence reached at position 14. Sentence: THISISSHORT
End of sentence reached at position 15. Sentence: THISISSHORT
End of sentence reached at position 15. Sentence: THISISASENTENCE
End of sentence reached at position 16. Sentence: THISISASENTENCE
End of sentence reached at position 16. Sentence: THISISSHORT
End of sentence reached at position 17. Sentence: THISISASENTENCE
End of sentence reached at position 17. Sentence: THISISSHORT
End of sentence reached at position 18. Sentence: THISISASENTENCE
End of sentence reached at position 18. Sentence: THISISSHORT
End of sentence reached at position 19. Sentence: THISISASENTENCE
End of sentence reached at position 19. Sentence: MOSLTYTHESAMELENGTHS

Desired output :

---

End of sentence reached at position 10. Sentence: THISISSHORT
End of sentence reached at position 14. Sentence: THISISASENTENCE
End of sentence reached at position 19. Sentence: MOSLTYTHESAMELENGTHS

Answer 1

You need to make copy of original list and then iterate over new copy and remove the items from original list

for item in list(original_list):
  ...
  original_list.remove(item)

In your case, code will look like below

total_read = 0

for i in range(21):
    random.shuffle(info)
    for index, value in enumerate(list(info)):
        b, p, s = value
        if len(s) <= i+1:
            print("Overshot! Shouldn't see this sentence anymore: %s" % (s))
            info.pop(index)
        print s[:i+1], i, s

        total_read += len(s[i + 1])

Answer 2

You can use del to delete the item from the zipped list

for i in range(21):
    q=0
    for p, b, s in info:
        if len(s)<=i+1:
            print(f'Overshot! Remove this element {s} {q}')
            del info[q]
        print(f"{s[:i+1]}, {i}, {s}")
        total_read += len(s[i+1])
        q+=1

Answer 3

Sanitize your input first and then loop over it:

sentences = ['THISISASENTENCE',
             'ANDHEREISONEMOREEXAMP',
             'ALLFROMDIFFERENTBOOKS',
             'ANDFROMDIFFERENTPAGES',
             'MOSLTYTHESAMELENGTHS',
             'THISISSHORT'
             ]
max_len = len(max(sentences, key=len))  # kudos ZachGates
print max_len  # 21
sentences = filter(lambda x: len(x)==max_len, sentences)
print sentences  # ['ANDHEREISONEMOREEXAMP', 'ALLFROMDIFFERENTBOOKS', 'ANDFROMDIFFERENTPAGES']

Now you can proceed as you did.

Answer 4

Make a copy of the list and iterate through the copy and delete the item from orginal.

for i in info[:]:
  info.remove(i)