table of Contents

Iterator

Iterator function is not just a call

Everything in python objects (data type)

Iterables: Data type comprising .__ iter__ method called iterables

In addition to numeric types, all data types are iterables

Iterator object: Object containing .__ iter__ and .__ next__ method is iterator object

Why should iterator object: to provide a means not dependent on the value of the index

for circulation principle (for loop is essentially a while loop, but is a certain controllable while loop)

 dic_iter = dic.__iter__()
# while True:
#     try:
#         print(dic_iter.__next__())
#     except StopIteration:
#         break

Iterables use iterator object into .__ iter__

Iterator .__ iter__ still using iterators

Iterables not necessarily the iterator object, the object must be an iterator iterable

A triplet of expressions

# if x > y:
#     print(x)
# else:
#     print(y)

A triplet of expressions - "three head expression

print(x) if x > y else print(y) #  --> 仅作了解

Go here if conditions are true condition is not satisfied the conditions else go here

List comprehensions

lt = [i**2 for i in range(10)]

from typing import Iterable # derive an iteration object type

print (isinstance (range (10), Iterable)) # determines whether the data type

Dictionary of formula

 dic = {i:i**2 for i in range(10)}
 
 zip()
# res = zip([1,2,3],[4,2,3,4,2,3,4,2,3],'abcadsfasdfasdf')  # res是一个迭代器,__next__返回元组
# print(res.__next__())  # type:tuple
# print(res.__next__())  # type:tuple
# print(res.__next__())  # type:tuple
# # print(res.__next__())  # type:tuple
 
 
 lt1 = ['a', 'b', 'c']
lt2 = [1, 2, 3]

dic = {k: v ** 2 for k, v in zip(lt1, lt2)}
print(dic)


lt = list('abc')
print(lt)

Generator formula

 generator 本质是一个迭代器 ---> 生成器: 本质就是迭代器,生成器就是一个自定义的迭代器


g = (i for i in range(10000000))
print(g)
# for i in g:
#     print(i)

lt = [i for i in range(10000000)]
print(lt)

Generator expressions: as the old hen, save memory space, use it to lay
the list comprehensions: as a basket of eggs, so take up memory space

Builder

# 生成器:含有yield关键字的函数叫做生成器
def ge():
    yield 3  # 一个yield相当于一个next; 暂停函数
    yield 4


# print(ge())  # ge()得到一个生成器 --> 生成器本质是迭代器
g = ge()  # 得到一个生成器

yield characteristics

Pause function
By next value

return characteristics

Termination function
Get value by calling the function

Write a range method

Builder
Vararg

What we lack, willy-nilly, dry hands

Recursion

# 传递 ; 回归


# 递归: 函数a内部直接调用函数a本身
# import sys
# sys.setrecursionlimit(10)
# print(sys.getrecursionlimit())
#
# def a():
#     x = 1
#     print(x)
#     a()
#
#
# a()

Each recursive, will not end function? No, and each recursive will open up memory space has been opened up if memory is blown up, so most recursive 1000

The real recursive have to have an exit condition

Recursion:

Internal calls the function yourself
There must be an exit condition
Recursive must have the law

day13 summary