itertools

问题 This question already has answers here : Test if a numpy array is a member of a list of numpy arrays, and remove it from the list (3 answers) Closed last year . With opencv , I'm detecting contours and selecting some of them: CNTS = [] _, contours, _ = cv2.findContours(gray, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE) for c in contours: if some_condition(c): CNTS.append(c) Then I'm looping over 2-subsets {c1, c2} of the list of contours, and removing some of them: TMP = CNTS[:] # copy it, to

问题 Suppose I have list_of_numbers = [[1, 2], [3], []] and I want the much simpler object list object x = [1, 2, 3] . Following the logic of this related solution, I do list_of_numbers = [[1, 2], [3], []] import itertools chain = itertools.chain(*list_of_numbers) Unfortunately, chain is not exactly what I want because (for instance) running chain at the console returns <itertools.chain object at 0x7fb535e17790> . What is the function f such that if I do x = f(chain) and then type x at the console

问题 I have a problem with 'flattening' out some generators in python. Here is my code: import itertools as it test = [[1,2,3],[4,5],[6,7,8]] def comb(possible): if len(possible) != 1: for a in possible[0]: yield from it.product((a,), comb(possible[1:])) else: yield from possible[0] list(comb(test)) which gives me: [(1, (4, 6)), (1, (4, 7)), (1, (4, 8)), (1, (5, 6)), (1, (5, 7)), (1, (5, 8)), (2, (4, 6)), (2, (4, 7)), (2, (4, 8)), (2, (5, 6)), (2, (5, 7)), (2, (5, 8)), (3, (4, 6)), (3, (4, 7)), (3

问题 In Python, how can I generate a string with all combinations of a set of characters up to a certain length? I know how to use itertools to generate all combinations and permutations, but I can't figure out how to generate strings of dynamic length. For example: a = [0,1] length = 4 Result: [0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1101, 1110, 1111] 回答1: You could use itertools.product : li = [] for i in itertools.product([0,1], repeat=4): li.append(''.join(map(str, i)))

问题 Can anyone explain to me, what exactly this code snippet is doing? chained_country_list = set(itertools.chain.from_iterable(country_and_countrycodes)) & set(all_countries) I know it runs two lists against each other, ending up with a set of unique values, that exists in both the lists it compares. But how it does it, and whats happening under the hood, confuses me. Would be a huge help if someone could share some light on the issue. 回答1: Let's break down each significant element of the code:

问题 How can I combine multiple lists starting at a specified index within one of the lists, while also summing the values at the respective indexes? If I had 3 lists: a = [1, 2, 3, 4, 5, 0, 0, 0, 0] b = [2, 3, 4, 5, 6] c = [5, 2] How could I make it so that I could insert lists b and c into any position within a , and the respective indexes would sum? For example, I could insert list b starting from the first index of a , and also insert list c starting from the fifth index of a . The output of

问题 I have a list that I use itertools.combinations to create all combinations. The elements in each list item are able to be delimited by the string ": ". I need to remove list items where there is more than one occurrence of the same matched substring in more than 1 element. The characters in the string up until ": " (delimiter to use for regex match???) needs to check each sub-element in a list item. Or, is there a better way? inList = [['TEST1: sub1'], ['TEST1: sub2'], ['TEST1: sub3'], [

问题 I'm working with some iterator generated using itertools.imap , and I was thinking if there is a way to access the iterator length inside the for-loop that I use to loop over the elements. What I can say for sure is that the iterator doesn't generate an infinite amount of data. Also, because the information I'm looping are from a query to a database, I can get the length of the information from there, but the function I'm using has to return an iterator. I thought of some options: def

问题 I have the following code which generates all possible combination that produces a given sum (n). This code, however, takes very long for large numbers (n). Is there a way I can parallelize my code across multiple processors? from itertools import combinations_with_replacement def all_combination(numbers, n): result = [seq for i in range(n, 0, -1) for seq in combinations_with_replacement(numbers,i) if sum(seq) == n] return result numbers = [1, 2, 3, 4, 5, 6] n=700 print len(all_combination

问题 I was going to generate some combination using the itertools, when i realized that as the number of elements increase the time taken will increase exponentially. Can i limit or indicate the maximum number of permutations to be produced so that itertools would stop after that limit is reached. What i mean to say is: Currently i have #big_list is a list of lists permutation_list = list(itertools.product(*big_list)) Currently this permutation list has over 6 Million permutations. I am pretty