Python——Python高阶函数（十）

1. lambda表达式（匿名函数）

# coding=utf-8
# lambda表达式（匿名函数）
# 计算圆形的面积
# pi * r * r
# 导入数学模块
import math
def circle_area(r):
    result = math.pi * r * r
    return result
r = circle_area(3)
print (r)
"""
lambda是一个关键字
冒号前边的r是这个函数的参数
冒号后边的是这个函数的运算逻辑
"""
result = lambda r:math.pi * r * r
r = result(3)
print (r)

def calc_function(o):
    if o == "+":
        return lambda a,b : a + b
    elif o == "-":
        return lambda a,b : a - b
    elif o == "*":
        return lambda a,b : a * b
    elif o == "/":
        return lambda a,b : a / b
f = calc_function("*")
print (f)
r = f(3,4)
print (r)

print打印结果：

28.2743338823
28.2743338823
<function <lambda> at 0x03159B70>
12

2. map自动拆分的计算函数

# coding=utf-8
# map函数
my_list = [1,2,3,4,5]
# 1
result = []
for i in my_list:
    result.append(i + 1)
print (result)

# 2
def add_one(e):
    return e + 1
r = map(add_one,my_list)
print (list(r))
def add_two(e):
    if e == 1:
        return e + 3
    elif e == 2:
        return 2 - 1
    else:
        return e
r =map(add_two,my_list)
print (list(r))
# 3
print (list(map(lambda e:e+1,my_list)))

print打印结果：

[2, 3, 4, 5, 6]
[2, 3, 4, 5, 6]
[4, 1, 3, 4, 5]
[2, 3, 4, 5, 6]

3. reduce自动堆叠计算函数

# coding=utf-8
# reduce
# 导入reduce
from functools import reduce
a =[2,4,6,8,10]
def add(x,y):
    return x + y
result = reduce(add,a)
print (result)

print (reduce(lambda x,y : x+y,a))

print打印结果：

30
30

4. filter过滤器函数

# coding=utf-8

# filter函数
letter=['a',"B",'c',"D",'e',"F"]
upper_letter = filter(lambda x: x == x.upper(),letter)
print (upper_letter)
print (list(upper_letter))

student_name = ['李元芳','李建国','莫怀羽']
print (list(filter(lambda x:x.startwith("李"),
                   student_name)))

print打印结果：

['B', 'D', 'F']
['B', 'D', 'F']
['李元芳','李建国']