Snippets for advanced generator research I used when figuring out an answer for https://stackoverflow.com/questions/74922314/yield-from-vs-yield-in-for-loop

gistfile1.txt

class VerboseItBase:
    def __new__(cls, gen, method):
        if method == "from":
            cls = VerboseItFrom
        elif method == "explicit":
            cls = VerboseItExplicit
        return super().__new__(cls)
    def __init__(self, gen, method):
        self.gen = gen
        self.method = method
    def __iter__(self):
        print("verbose iter called for 'classic'")
        try:
            for item in self.gen:
                yield item
        except GeneratorExit:
            print("generator exit thrown in intermediate gen. 'classic'")
            raise
        
    def close(self):
        print("close in intermediate iterator called")
        # Explictly do not forward close for testing purposes:
        # self.gen.close()
    def __del__(self):
        print("intermediate iterator __del__")
        try:
            super().__del__()
        except AttributeError:
            pass
        
VerboseIt = VerboseItBase

class VerboseItExplicit(VerboseItBase):
    def __iter__(self):
        print("verbose iter called for 'explict'")
        return self
    def throw(self, *args):
        print(args)
    def __next__(self):
        print("intermediate __next__ called")
        return next(self.gen)


class VerboseItFrom(VerboseItBase):
    def __iter__(self):
        print("verbose iter called for 'yield from'")
        try:
            yield from self.gen
        except GeneratorExit:
            print("generator exit thrown in intermediate gen. 'from'")
            raise
        return
    
class Test:
    def __init__(self, gen, method):
        self.gen = gen
        self.method = method
    def __iter__(self):
        return iter(VerboseIt(self.gen, self.method))


first = lambda i: next(iter(i))

a = Test((i for i in range(3)), "")