python学习笔记（6）匿名函数等

from functools import reduce
# 列表推导式：[表达式 for 变量 in 数据列表 if 表达式]
# 一行打印1~100之间的偶数
l = [i for i in range(1,101) if i % 2 == 0]
print(l)
# 1到100所有平方的列表
l = [i * i for i in range(1,101)]
print(l)

# 字典推导式
# {字典内容 + 循环条件 + 判断条件}
# {"a":1,"b":2,"c":3}要求将键值倒置
dic = {"a":1,"b":2,"c":3}
l = {v : k for k, v in dic.items()}
print(l)

# 新字典数值平方
l = {k : v * v for k, v in dic.items()}
print(l)

# 新字典数值平方,key大写
l = {k.upper() : v * v for k, v in dic.items()}
print(l)

# 匿名函数
bar = lambda x,y:x+y
ret = bar(3,1)
print(ret)

ret = (lambda x,y:x+y)(3,1)
print(ret)

# 高阶函数：filter map reduce
l = [1,2,3,4,5,6,7,8]
# 保留所有的偶数
# 方法1
l1 = [i for i in l if i % 2 == 0]
print(l1)
# 方法2
def funca(item):
    if item % 2 == 0:
        return True
    else:
        return False
l1 = list(filter(funca,l))
print(l1)
# 方法3
l1 = list(filter(lambda i : i % 2 == 0,l))
print(l1)

# 计算列表平方
# 方法1
def bar(item):
    return item * item

l1 = list(map(bar, l))
print(l1)
# 方法2
l1 = list(map(lambda i : i * i, l))
print(l1)

# 计算1~100的和(reduce)
# 方法1
ret = sum([i for i in range(1,101)])
print(ret)
# 方法2
def func(x,y):
    return x+y
ret = reduce(func, [i for i in range(1,101)])
print(ret)
# 方法3
ret = reduce(lambda x,y:x+y,range(1,101))
print(ret)

# 按照index = 1从大到小排序
l = [("yuan",22),("yuan1",21),("yuan2",25)]
l1 = sorted(l,key = lambda i:i[1],reverse=True)
print(l1)
# 按照value从大到小排序
l = [{"age":22},{"age":33},{"age":29}]
l1 = sorted(l,key= lambda i : i["age"],reverse=True)
print(l1)

# zip函数
l1 = [1,2,3]
l2 = (4,5,6)
l = list(zip(l1,l2))
print(l)  # [(1, 4), (2, 5), (3, 6)]

name = ["yuan","rain","alvin"]
ages = [18, 22, 33]

l = list(zip(name,ages))
print(l)  # [('yuan', 18), ('rain', 22), ('alvin', 33)]
ret = dict(l)
print(ret)  # {'yuan': 18, 'rain': 22, 'alvin': 33}