yield

问题 I want to write a Python generator function that never actually yields anything. Basically it's a "do-nothing" drop-in that can be used by other code which expects to call a generator (but doesn't always need results from it). So far I have this: def empty_generator(): # ... do some stuff, but don't yield anything if False: yield Now, this works OK, but I'm wondering if there's a more expressive way to say the same thing, that is, declare a function to be a generator even if it never yields

问题 I want to write a Python generator function that never actually yields anything. Basically it's a "do-nothing" drop-in that can be used by other code which expects to call a generator (but doesn't always need results from it). So far I have this: def empty_generator(): # ... do some stuff, but don't yield anything if False: yield Now, this works OK, but I'm wondering if there's a more expressive way to say the same thing, that is, declare a function to be a generator even if it never yields

问题 I am trying to create a custom data generator and don't know how integrate the yield function combined with an infinite loop inside the __getitem__ method. EDIT : After the answer I realized that the code I am using is a Sequence which doesn't need a yield statement. Currently I am returning multiple images with a return statement: class DataGenerator(tensorflow.keras.utils.Sequence): def __init__(self, files, labels, batch_size=32, shuffle=True, random_state=42): 'Initialization' self.files

问题 I'm trying to convert a chunk of Ruby code into Node.js. One particular piece has me stumped, concerning yield . The code goes like this: each_pair(hash["args"][0]) do |key, value, pair| # perform operations end ... def each_pair(hash) hash["props"].each do |p| yield(p["key"], p["value"], p) end end If I am reading this code correctly, it's saying "Iterate over the hash properties. For every element, call back out to the outer function and perform the operation with the given p["key"], p[

问题 I read here the following example: >>> def double_inputs(): ... while True: # Line 1 ... x = yield # Line 2 ... yield x * 2 # Line 3 ... >>> gen = double_inputs() >>> next(gen) # Run up to the first yield >>> gen.send(10) # goes into 'x' variable If I understand the above correctly, it seems to imply that Python actually waits until next(gen) to "run up to" to Line 2 in the body of the function. Put another way, the interpreter would not start executing the body of the function until we call

问题 I am trying to use the drawer to navigate (yield) to the same class (CategoryListPage) with different parameters it doesnt seem to update the widget page. but if I go HomePage then yield CategoryListPage(), it works. What can I do to navigate to the same class, is there a way to refresh the content ? here is my code: class NavigationBloc extends Bloc<NavigationEvents, NavigationStates> { @override NavigationStates get initialState => HomePage(); @override Stream<NavigationStates>

问题 Is there a one-line expression for: for thing in generator: yield thing I tried yield generator to no avail. 回答1: In Python 3.3+, you can use yield from. For example, >>> def get_squares(): ... yield from (num ** 2 for num in range(10)) ... >>> list(get_squares()) [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] It can actually be used with any iterable. For example, >>> def get_numbers(): ... yield from range(10) ... >>> list(get_numbers()) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> def get_squares(): ... yield

问题 Is there a one-line expression for: for thing in generator: yield thing I tried yield generator to no avail. 回答1: In Python 3.3+, you can use yield from. For example, >>> def get_squares(): ... yield from (num ** 2 for num in range(10)) ... >>> list(get_squares()) [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] It can actually be used with any iterable. For example, >>> def get_numbers(): ... yield from range(10) ... >>> list(get_numbers()) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> def get_squares(): ... yield

问题 The question "Meaning of the word yield" mentions the Enumerator::Yielder#yield method. I haven't used it before, and wonder under what circumstances it would be useful. Is it mainly useful when you want to create an infinite list of items, such as the Sieve of Eratosthenes, and when you need to use an external iterator? 回答1: "How to create an infinite enumerable of Times?" talks about constructing and lazy iterators, but my favorite usage is wrapping an existing Enumerable with additional

问题 I want to extract from Iterable[Try[Int]] a list of all valid values ( Iterable[Int] ) val test = List( Try(8), Try(throw new RuntimeException("foo")), Try(42), Try(throw new RuntimeException("bar")) ) The following is the way to print all valid values from test : for { n <- test p <- n } println(p) // Output // 8 // 42 However, when I tried to save the valid values to list I have received an error: val nums: Seq[Int] = for { n <- list p <- n // Type mismatch. Required: IterableOnce[Int],