• python 函数


    函数的使用

    形参,实参

    import  time
    
    # 创建logger函数,等待传入的值为,形参
    def logger(date):
    
        print("starting action1")
        with open("log.txt","a") as f:
            f.write("end save date: %s
    " %date)
    
    # 传入的值为,实参
    logger(time.strftime("%Y-%m-%d %X"))


    必须参数

    必须要,对应,传入数量也必须一样
    def print_info(name,age):
        print("name:%s" % name)
        print("age:%s" % age)
    print_info("Kidd",16)

     

    关键词参数

    根据形参的参数,来传实参
    def print_info(name,age):
        print("name:%s"%name)
        print("age:%s"%age)
    print_info(age=16,name="Kidd")

    默认参数

    给形参传默认值,默认值形参,必须放到形参的最后

    # 使用默认参数
    def print_info(name,age=18):
        print("name:%s"%name)
        print("age:%s"%age)
    print_info("Kidd")
    
    
    # 不使用默认参数
    def print_info(name,age=18):
        print("name:%s"%name)
        print("age:%s"%age)
    print_info(age=16,name="Kidd")

    不定长参数

    传入任意数量的实参  *

    传入任意数量的关键词实参  **

    def function(name="Bob",*args,**kwargs):
        print(name)
        print(*args)
        for key in kwargs:
            print("%s:%s"%(key,kwargs[key]))
    function("Kidd",1,2,3,age=16,sex="")
    
    
    运行结果:
    Kidd
    1 2 3
    age:16
    sex:男

    实参传入* , **

    # 实参传 * 将列表,元祖中的元素提取出来
    def func(*args):
        print(args) # (1, 2, 3, 4, 5, 6, [7,8,9])
    func(*(1,2,3,),*[4,5,6],[789])
    
    
    # 实参传 ** 将关键字传参,替换成了字典传参
    def func1(**kwargs):
        print(kwargs)
    student1 = {"一斑":{"小明":{"age":15},"小红":{"age":14}}}
    student2 = {"二班":{"小李":{"age":15},"小张":{"age":16}}}
    func1(**student1,**student2)
    
    # {'一斑': {'小明': {'age': 15}, '小红': {'age': 14}}, '二班': {'小李': {'age': 15}, '小张': {'age': 16}}}

    return

    作用:函数的结束,函数的返回值

    # return默认值None
    def function(*args):
        number = sum(args)
        print(number) # 6
    number = function(1,2,3)
    print(number) # None
    
    
    
    # 使用return
    def function(*args):
        number = sum(args)
        return number
    number = function(1,2,3)
    print(number) # 6
    
    
    
    # 返回多个数
    def function(*args):
        number = sum(args)
        return number,7,[6,7],"6,7"
    number = function(1,2,3)
    
    # 返回一组元祖
    print(number) # (6, 7, [6, 7], '6,7')

    作用域

    python的作用域,一共分为4种,分别是built,global,enclosing,local

    x = int(2.0) # int built-in
    count = 0 # global
    def father():
        father_name = "father" # enclosing
        def son():
            son_name = "son" # local

    高阶函数

    1、函数名可以参数输入

    2、函数名可以作为返回值

    def first_portion(n):
        return n * n
    def second_portion(one,two,other):
        result = other(one) + other(two)
        return result
    print(second_portion(1,2,other=first_portion)) # 5

    闭包 

    闭包 = 函数 + 定义函数时的环境

    def outside(num):
        def inside():
            print(num)
        return inside
    out = outside(10)
    out()

    递归函数

    #阶乘
    
    #使用 for 循环
    def multiply(n):
        number = 1
        for i in range(1,n+1):
            number = i * number
        return number
    mul = multiply(5)
    print(mul) # 120
    
    
    
    #使用递归
    def multiply(n):
        if n == 1:
            return 1
        return n * multiply(n-1)
    mul = multiply(5)
    print(mul) # 120
    
    
    
    # 使用reduce 和 lambda
    from functools import reduce
    mul = reduce(lambda a,b : a*b,range(1,6))
    print(mul)

     使用递归,要有一个明确的结束条件,

    递归的效率低,不如for循环

    def addition(n):
        if n <= 2:
            return n
        return addition(n-1) + addition(n-2)
    add = addition(1)
    print(add)

     斐波那契数列

    def func(n):
        b,a,v = 0,1,0
        for i in range(n):
            v = a + b
            b = a
            a = v
            print(a)
    func(5)
    
    
    def func1(n):
        b, a = 0, 1
        for i in range(n):
            b,a = a,a+b
            print(a)
    func1(5)

    两个结果一样,根据规律,使用最简单的

    内置函数

    filter(function,iterable)

    # filter函数,相当于过滤器
    iter_object = [1,2,3,4,5]
    def filter_function(num):
        if num > 1:
            return num
    object = filter(filter_function,iter_object)
    print(list(object)) # [2, 3, 4, 5]

    map(func,iter1,iter2)

    会根据提供的函数对指定序列做映射。

    iter_name = ["小明:","小张:","小李:"] iter_sex = ["","",""] def map_function(iter1,iter2): return iter1 + iter2 iter_content = map(map_function,iter_name,iter_sex) print(list(iter_content)) # ['小明:男', '小张:女', '小李:男']

    reduce(function,sequence)

    对参数序列中元素进行累积

    from
    functools import reduce def add(x,y): return x + y num = reduce(add,range(1,101)) print(num) # 5050

    lambda

    lambda 匿名函数,它是一个表达式
    用法: 参数 : 返回值
    mul = reduce(lambda x,y:x*y,range(1,6))
    print(mul) # 120
    
    filter_lambda = filter(lambda a : a>1,range(1,6))
    print(list(filter_lambda)) # [2, 3, 4, 5]
    
    map_lambda = map(lambda a : a ** 2,range(1,6))
    print(list(map_lambda)) # [1, 4, 9, 16, 25]

    chr

    chr() 用一个范围在 range(256)内的(就是0~255)整数作参数,返回一个对应的字符。

    其中 A-Z 对应的数值为 65-90

    其中 a-z 对应的数值为 97 -122

    for i in range(256):
        if chr(i) == "A":
            print(i) # 65
        elif chr(i) == "a":
            print(i) # 97

    ord

    Given a string representing one Unicode character, return an integer representing the Unicode code point of that character. For example, ord('a') returns the integer 97 and ord('€') (Euro sign) returns 8364. This is the inverse of chr().

    ord('a') #97

    enumerate(iterablestart=0)

    Return an enumerate object. iterable must be a sequence, an iterator, or some other object which supports iteration. The __next__() method of the iterator returned by enumerate() returns a tuple containing a count (from start which defaults to 0) and the values obtained from iterating over iterable.

    for n,i in enumerate(range(1,10),1):
        print(n,i)

    eval(expressionglobals=Nonelocals=None)

    The arguments are a string and optional globals and locals. If provided, globals must be a dictionary. If provided, locals can be any mapping object.

    x = 1
    eval('x+1') #2

    pow(xy[, z])

    Return x to the power y; if z is present, return x to the power y, modulo z (computed more efficiently than pow(x, y) z). The two-argument form pow(x, y) is equivalent to using the power operator: x**y.

    pow(2,2) # 4
    pow(2,2,3) # 1

    More

    https://docs.python.org/3/library/functions.html

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  • 原文地址:https://www.cnblogs.com/py-peng/p/10755317.html
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