1, the generator
(1) What is a generator?
Core: the nature of the generator is a iterator
Iterator is built-in
Builder programmer to write an iterator
def func():
print("这是一个函数")
return "函数"
func()
def func():
print("这是一个生成器")
yield "生成器"(2) the preparation of the pattern generator:
<1> based on a function written
<2> derivations prepared
(3) a generator function:
Constructed by the generator function generator
<1> yield representative of the body appears to declare a function generator (generator - Generator)
<2> corresponds to a yield a next ()
def func():
msg = input("请输入内容")
yield msg
print("这是第二次启动")
yield "生成器2"
yield "生成器3"
yield "生成器4"
g = func()
print(next(g))
print(next(g))
print(next(g))
print(next(g))
# 生成器的本质就是迭代器.迭代器如何取值，生成器就如何取值<3> yield and return the difference between:
1> same point:
Content is returned
You can return multiple, but the return will only execute a written multiple
2> differences:
return termination function generator yield is suspended
yield the current execution location can be recorded
Action (4) generator: space-saving
(5) usage scenarios:
When a large amount of data files or containers, it is recommended to use the generator
(6) What is the difference between iterators, what is the builder?
<1> through the address:
Iterator address: <list_iterator object at 0x000000987B6E97F0>
Address generator: <generator object func at 0x00000087C2A10CA8>
<2> by a send () method: (send () method must first send None)
Do not send () method is iterator
With a send () method is the generator
def func():
a = yield 1
print(a)
b = yield 2
print(b)
g = func()
print(g.send(None)) # send -- 发送
print(g.send("alex")) # send -- 发送
print(g.send("宝元")) # send -- 发送. 1> Send and next () difference:
The same point:
send and next () so that the generator can yield a corresponding downward once.
Yield value can be obtained is generated.
Differences:
The first acquisition yield values can only be used next can not send (can send (None)).
can send to yield a set value is transmitted.
(7) yield and the yield from the difference between:
The yield iterables a one-time return
yield from the iterable returned one by one
def func():
def foo():
print(11)
lst = {"key":1,"key1":2}
yield foo
print(func().__next__())
def func():
lst = [1,2,3,45,6]
lst1 = ["alex","wusir","taibi","baoyuan"]
yield from lst
yield from lst1
g = func()
for i in g:
print(i)
lst = [1,2,3,45,6]
lst1 = ["alex","wusir","taibi","baoyuan"]
for i in lst,lst1:
print(i)(8) iterables, comparator iterators, generator:
Iterables
Advantage: list, tuple .str save time, convenient value, flexible (with its own private method)
Disadvantages: consume a lot of memory
Iterator
Benefits: save space
Disadvantages: can not directly see the value, use inflexible, time-consuming, one-time, non-retrograde
Builder
Advantages: saving space, arbitrarily defined
Disadvantages: can not directly see the value, time-consuming, one-time, non-retrograde