1、推导式
推导式又叫做解析式，是简化冗余代码实质有效的方法，Python中实用的语法糖，可以分为以下几类：
- 列表推导式（⭐）
- 字典推导式（⭐）
- 集合推导式
- 元祖推导式
下面只介绍常用的列表推导式和字典推导式。
1.1 列表推导式
对列表中每个元素进行一定操作。
基本使用
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| list = [1,2,3,4,5,6,7,8,9,10]
list1 = [x+2 for x in list]
print(list1)
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条件表达式
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| list = ["Bob","Jason","Peter","Jani","Tom"]
list1 = [name+"666" for name in list if len(name) > 3]
print(list1)
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多个 for 循环
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| time = ['%.2d:%.2d'%(h,m )for h in range(24) for m in range(0,60,5) ]
print(time)
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多个 for 循环+条件表达式
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| list = [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]
print(list)
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1.2 字典推导式
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| listdemo = ["Bob","Jason","Peter","Jani","Tom"]
newdict = {key:len(key) for key in listdemo}
print(newdict)
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互换 key 和 value 的值
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| person = {'角色名':'宫本武藏','定位':'刺客'}
person_reverse = {k:v for v,k in person.items()}
print(person_reverse)
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2、字典遍历
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| person = {'角色名':'宫本武藏','定位':'刺客'}
for key,value in person.items():
print(key,value)
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3、判断元素是否在列表中
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| listdemo = ["Bob","Jason","Peter","Jani","Tom"]
if "Peter" in listdemo:
print("Yes")
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4、反转字符串
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| name = "Tom"
reverse_name = name[::-1]
print(reverse_name)
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5、反转列表
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| name_list = ["Bob","Jason","Peter","Jani","Tom"]
reverse_name_list = name_list[::-1]
print(reverse_name_list)
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6、获取时间
获取当前时间
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| import datetime
current_time = datetime.datetime.now()
print(current_time)
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获取当前日期
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| import datetime
current_date = datetime.date.today()
print("当前日期:", current_date)
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获取毫秒级时间（程序执行时间）
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| import time
start_time = time.time()
numbers = [i for i in range(1000000)]
end_time = time.time()
time_ = end_time - start_time
print(time_)
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7、三元运算符
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| a = 1
b = 2
max = a if a>b else b
print(max)
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8、枚举循环
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| fruits = ['apple','banana']
for index,fruit in enumerate(fruits):
print(index,fruit)
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