2012年1月27日 · If you skip the end index, like in your question, it would take elements from the start index (x), pick every yth element until it reaches the end of the list if y is positive and beginning of the list if y is negative. E.g. l[1::-1] = [2,1] l[1::2] = [2,4,6] The default step size is 1.

If you want to see the dependency with the length of the list n: Pure python. I tested for list length up to n=10000 and the behavior remains the same. So the integer multiplication method is the fastest with difference. Numpy. For lists with more than ~300 elements you should consider numpy. Benchmark code:

joined_list = [item for list_ in [list_one, list_two] for item in list_] It has all the advantages of the newest approach of using Additional Unpacking Generalizations - i.e. you can concatenate an arbitrary number of different iterables (for example, lists, tuples, ranges, and generators) that way - and it's not limited to Python 3.5 or later.

2013年3月20日 · Working on a python assignment and was curious as to what [:-1] means in the context of the following code: instructions = f.readline()[:-1] Have searched on here on S.O. and on Google but to no avail.

@Macke: Note: As of Python 3.3, lists do provide clear and copy methods, equivalent to doing del mylist[:] or mylist[:] respectively. They're not required on mutable sequences in general, so if you might receive an arbitrary mutable sequence, you'd want to stick to slice based operations, but the named methods are at least available on list.

2013年8月16日 · That is a list in Python 2.x and behaves mostly like a list in Python 3.x. If you are running Python 3 and ...

2016年12月3日 · A list of lists named xss can be flattened using a nested list comprehension: flat_list = [ x for xs in xss for x in xs ] The above is equivalent to: flat_list = [] for xs in xss: for x in xs: flat_list.append(x) Here is the corresponding function: def flatten(xss): return [x …

2018年9月19日 · All your return c.most_common()[-1] statement does is call c.most_common and return the last value in the resulting list, which would give you the least common item in that list. Essentially, this line is equivalent to:

2009年5月30日 · The simplest way to display last element in python is >>> list[-1:] # returns indexed value [3] >>> list[-1] # returns value 3 there are many other method to achieve such a goal but these are short and sweet to use.

2009年11月11日 · Besides len you can also use operator.length_hint (requires Python 3.4+). For a normal list both are equivalent, but length_hint makes it possible to get the length of a list-iterator, which could be useful in certain circumstances: