推導式

通過一行回圈判斷遍歷出一些列資料的方法叫做推導式

語法:
　　val for val in iterable

1.推導式基本語法

lst = []
for i in range(1,51):
    lst.append(i)
print(lst)

改寫推導式

lst = [  i for i in range(1,51)  ]
print(lst)

小練習

# 1.[1,2,3,4,5] => [2,4,6,8,10]
lst = [ i*2 for i in range(1,6) ]
print(lst)

2.帶有判斷條件的推導式

注意點:for后面緊跟的判斷條件只能是單項分支.
[1,2,3,4,5,6,7,8,9,10] => [1,3,5,7,9 ... ]

lst = [1,2,3,4,5,6,7,8,9,10]
lst_new = []
for i in lst:
    if i % 2 == 1:
        lst_new.append(i)
print(lst_new)

改寫推導式

lst = [ i for i in lst if i % 2 == 1 ]
print(lst)

3.多回圈推導式 # 誰????誰

lst1 = ["孫杰龍","陳露","曹靜怡"]
lst2 = ["王志國","鄧鵬","合理"]
lst_new = []
for i in lst1:
    for j in lst2:
        lst_new.append(i+"????"+j)
print(lst_new)

改寫推導式

lst = [ i+"????"+j for i in lst1 for j in lst2 ]
print(lst

4.帶有判斷條件的多回圈推導式

lst_new = []
for i in lst1:
    for j in lst2:
        if lst1.index(i) == lst2.index(j):
            lst_new.append(i+"????"+j)
print(lst_new)

改寫推導式

lst = [i+"????"+j for i in lst1 for j in lst2 if lst1.index(i) == lst2.index(j)]
print(lst)

集合推導式

案例:
　　滿足年齡在18到21,存款大于等于5000 小于等于5500的人,
　　開卡格式為:尊貴VIP卡老x(姓氏),否則開卡格式為:摳腳大漢卡老x(姓氏)
　　把開卡的種類統計出來

lst = [
    {"name":"趙沈陽","age":18,"money":3000},
    {"name":"趙萬里","age":19,"money":5200},
    {"name":"趙蜂擁","age":20,"money":100000},
    {"name":"趙世超","age":21,"money":1000},
    {"name":"王志國","age":18,"money":5500},
    {"name":"王永飛","age":99,"money":5500}
]
setvar = set()
for i in lst:
    print(i) # {'name': '趙沈陽', 'age': 18, 'money': 3000}
    if 18 <= i["age"] <= 21 and 5000 <= i["money"] <= 5500:
        res = "尊貴VIP卡老{}".format(i["name"][0])
    else:
        res = "摳腳大漢卡老{}".format(i["name"][0])
    # 添加到集合中
    setvar.add(res)
print(setvar)

{ 三元運算子 + 推導式 }

setvar = { "尊貴VIP卡老{}".format(i["name"][0]) if 18 <= i["age"] <= 21 and 5000 <= i["money"] <= 5500 else "摳腳大漢卡老{}".format(i["name"][0]) for i in lst }
print(setvar)

字典推導式

一.enumerate

enumerate(iterable,[start=0])
功能:列舉 ; 將索引號和iterable中的值,一個一個拿出來配對組成元組,通過迭代器回傳
引數:
　　iterable: 可迭代性資料 (常用:迭代器,容器型別資料,可迭代物件range)
　　start: 可以選擇開始的索引號(默認從0開始索引)
回傳值:迭代器

基本語法

from collections import Iterator,Iterable
lst =["王文","呂洞賓","何仙姑","鐵拐李","張國老","曹國舅","藍采和","韓湘子"]
it = enumerate(lst)
it = enumerate(lst,start=100)
print(isinstance(it,Iterator))

next

print( next(it) )

for + next (推薦,資料較大時使用)

for i in range(3):
    print(next(it))

for

for i in it:
    print(i)

list 強轉迭代器

print(list(it))

(1) 字典推導式 配合 enumerate 來實作

dic = {k:v for k,v in enumerate(lst,start=100)}
print(dic)
"""
(100, '王文')
(101, '呂洞賓')
(102, '何仙姑')
(103, '鐵拐李')
(104, '張國老')
(105, '曹國舅')
(106, '藍采和')
(107, '韓湘子')
"""

(2) 使用dict強轉迭代器,瞬間得到字典

dic = dict( enumerate(lst,start=100) )
print(dic)

二.zip

特點:按照索引配對
zip(iterable, ... ...)
　　功能: 將多個iterable中的值,一個一個拿出來配對組成元組,通過迭代器回傳
　　iterable: 可迭代性資料 (常用:迭代器,容器型別資料,可迭代物件range)
回傳: 迭代器

基本語法

# lst1 = ["孫開啟","王永飛","于朝志"]
# lst2 = ["薛宇健","韓瑞曉","上朝氣"]
# lst3 = ["劉文博","歷史園","張光旭"]

# 在索引下標同時存在時,才會進行配對,否則舍棄.
lst1 = ["孫開啟","王永飛","于朝志"]
lst2 = ["薛宇健","韓瑞曉"]
lst3 = ["劉文博"]

it = zip(lst1,lst2,lst3)
print(list(it))

(1) 字典推導式 配合 zip 來實作

lst_key = ["ww","axd","yyt"]
lst_val = ["王維","安曉東","楊元濤"]

# ('ww', '王維'), ('axd', '安曉東'), ('yyt', '楊元濤')
dic = {k:v   for k,v in zip(lst_key , lst_val) }
print(dic)

(2) 使用dict強轉迭代器,瞬間得到字典

dic = dict( zip(lst_key , lst_val) )
print(dic)

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