Question

我有这样的守则:

class A:
  def __iter__(self):
    for i in range(100):
      yield i

class B:
  def __init__(self, src):
    self.src = src
  def __iter__(self):
    for i in self.src:
      yield i * 2

class C:
  def __init__(self, src1, src2):
    self.src1 = src1
    self.src2 = src2
  def __iter__(self):
    for i, j in zip(self.src1, self.src2):
      yield i + j

a = A()
b = B(a)
c = C(a, b)
it = iter(c)
next(it)

我想做的是,在援引<代码>next(it)时,对电话链进行校正。更具体地说,我想在每一类别中在<代码>yield后执行一些新的代码,而不必修改等级代码。理想的是,实施<代码>yield的新代码打印。这是可能的吗?

Answer 1

You can create a subclass for each of the generator class with a wrapper __iter__ method that prints in which class yield is to be executed before yielding from the __iter__ method of the superclass. Since yield pauses the execution of the generator and returns control back to the caller, the wrapper should print such an output before, not after, yielding:

def print_yields(cls):
    class wrapper(cls):
        def __iter__(self):
            iterator = super().__iter__()
            for i in iterator:
                print(f yielding {i} from class {cls.__name__} with iterator {id(iterator):x} )
                yield i
    return wrapper

a = print_yields(A)()
b = print_yields(B)(a)
c = print_yields(C)(a, b)
for i in c:
    print(i)

Demo: https://replit.com/@blhsing/UprightWebbedArtificialintelligence

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