generator

问题 I am very very new to Python 3, so please be nice. I have looked at all the documentation I could find regarding this - there does seem to be a lot, it's just I still cannot figure out what to do. This is my code: poly = [[36606.0,53223.0],[37332.0,52224.0],[39043.0,53223.0], [41603.0,53223.0],[42657.0,53278.0],[43123.0,52060.0], [44054.0,51156.0],[45806.0,51498.0],[46751.0,53237.0], [46983.0,54606.0],[45861.0,57057.0],[44971.0,58836.0], [44054.0,60616.0],[43451.0,58138.0],[41850.0,59179.0],

问题 Suppose I have a list of sets and I want to get the union over all sets in that list. Is there any way to do this using a generator expression? In other words, how can I create the union over all sets in that list directly as a frozenset ? 回答1: Just use the .union() method. >>> l = [set([1,2,3]), set([4,5,6]), set([1,4,9])] >>> frozenset().union(*l) frozenset([1, 2, 3, 4, 5, 6, 9]) This works for any iterable of iterables. 回答2: I assume that what you're trying to avoid is the intermediate

问题 I'm trying to build a simple REST API with Koa.js. It uses ES6 generator functions, which I find much more pleasant than callbacks (they're just like C#'s async-await). The yield keyword expects a thenable (promise, thunk, generator). I'm using Bluebird's promisifyAll method to promisify callback libraries (request in my case), but I still keep getting error. Here are my code and the error: var koa = require('koa') , route = require('koa-route') , app = module.exports = koa() , Promise =

问题 I have a question regarding converting a yield statement to a generator expression So I have this small yield method that gets a function and a starting number as its inputs, and basically calls the function for each previous number that was called i.e: The first call returns the initial number The second call returns the function(initial number) The third call returns the function(second number) The fourth call returns the function(third number) etc. Here is the code in Python: def some_func

问题 I have a file like this: 1 2 3 TAB 1 2 3 TAB I want to read the lines between TAB as blocks. import itertools def block_generator(file): with open(file) as lines: for line in lines: block = list(itertools.takewhile(lambda x: x.rstrip('\n') != '\t', lines)) yield block I want to use it as such: blocks = block_generator(myfile) for block in blocks: do_something(block) The blocks i get all start with the second line like [2,3] [2,3] , why? 回答1: Here is another approach using groupby from

问题 Is it possible to create a iterator/generator which will decide on the next value based on some result on the previous iteration? i.e. y = None for x in some_iterator(ll, y): y = some_calculation_on(x) I would like the logic of choosing the next x to depend on the calculation result allowing different logic for different results, much like in a search problem. I also want to keep the how to choose the next x and the calculation on x as separate as possible. 回答1: Did you that you can send to a

问题 I have a an array of objects and would like to be able to randomly choose one from the list when a button is pressed. How would you do that in Android? 回答1: Do something like this inside your onClickListener Random rand = new Random(); int selector = rand.nextInt(yourList.length); yourList.get(selector); Something like that. EDIT: Actually if it is an ArrayList then it will be more like this Random rand = new Random(); int selector = rand.nextInt(yourList.size()); yourList.get(selector); 回答2:

问题 The following code only prints "good". Why the generator function is not executed? I noticed with pdb that after executing 'handlers1' the script reaches the line with f1's definition but then does not get inside the function. Conversely, it's returned 'GeneratorExit: None'. class foo: def f0(self, s): print s def f1(self, s): print "not " + s yield 1 def run(self): handlers={0 : self.f0, 1 : self.f1} handlers[0]('good') handlers[1]('good') bar = foo() bar.run() Why this happens? Is it

问题 An interview question for a .NET 3.5 job is "What is the difference between an iterator and an enumerator"? This is a core distinction to make, what with LINQ, etc. Anyway, what is the difference? I can't seem to find a solid definition on the net. Make no mistake, I can find the meaning of the two terms but I get slightly different answers. What would be the best answer for an interview? IMO an iterator "iterates" over a collection, and an enumerator provides the functionality to iterate,

问题 Say I have N generators that produce a stream of items gs = [..] # list of generators . I can easily zip them together to get a generator of tuples from each respective generator in gs : tuple_gen = zip(*gs) . This calls next(g) on each g in sequence in gs and gathers the results in a tuple. But if each item is costly to produce we may want to parallelize the work of next(g) on multiple threads. How can I implement a pzip(..) that does this? 回答1: What you asked for can be achieved by creating