python - How do I make a flat list out of a list of lists? - Stack …
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 …
How do I concatenate two lists in Python? - Stack Overflow
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.
python - How do I clone a list so that it doesn't change …
@loved.by.Jesus: Yeah, they added optimizations for Python level method calls in 3.7 that were extended to C extension method calls in 3.8 by PEP 590 that remove the overhead of creating a bound method each time you call a method, so the cost to call alist.copy() is now a dict lookup on the list type, then a relatively cheap no-arg function call that ultimately invokes the same thing …
Best and/or fastest way to create lists in python
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:
Identify duplicate values in a list in Python - Stack Overflow
list.count() is a O(N) job (all elements in the list are compared to count) and you are doing this in a loop over N elements, giving you quadratic performance, O(N^2). So for a 10-element list 100 steps are executed, for a 1000 element list 1 million, etc.
python - What does list[x::y] do? - Stack Overflow
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.
python - Best way to remove elements from a list - Stack Overflow
2014年2月2日 · Python’s lists are variable-length arrays, not Lisp-style linked lists. The implementation uses a contiguous array of references to other objects, and keeps a pointer to this array. This makes indexing a list a[i] an operation whose cost is independent of the size of the list or the value of the index.
python - How do I get the last element of a list? - Stack Overflow
2019年6月14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.
python - How do I count the occurrences of a list item? - Stack …
2010年4月8日 · Given a single item, how do I count occurrences of it in a list, in Python? A related but different problem is counting occurrences of each different element in a collection, getting a dictionary or
Get unique values from a list in python - Stack Overflow
2012年10月15日 · If you really want to have a vanilla python list back, you can always call list(). However, the result is automatically sorted, as you can see from the above code fragments. Check out numpy unique without sort if retaining list order is required.