//区别于列表生成式 gen = [x*x for x in range(5)]
gen = (x*x for x in range(5)) 
print(gen) //Out:<generator object <genexpr> at 0x00000258DC5CD8E0>

def fib():
  prev, curr = 0, 1
  while True:
    yield curr
    prev, curr = curr, curr + prev
f = fib()
print(f) //Out:<generator object fib at 0x00000258DC5CD150>

print(next(gen)) //0
print(next(gen)) //1
...
print(next(gen)) //16
print(next(gen)) //StopIteration

for n in gen:
  print(n) //0 1 4  9 16

class Fib:
  def __init__(self):
    self.prev = 0
    self.curr = 1
 
  def __iter__(self):
    return self
 
  def __next__(self):
    value = self.curr
    self.curr += self.prev
    self.prev = value
    return value
f = Fib() 
count = 1 
for n in f:
  print(n)
  count = count+1
  if count>=10:
    break
//Out:1 1 2 3 5 8 13 21 34

demo = [1,2,3,4]
print(isinstance(demo, Iterable)) //True
iter_object = iter(demo)
print(iter_object) //<list_iterator object at 0x00000258DC5EF748>