python函数，,一、函数：创建函数：

python函数，,一、函数：创建函数：

一、函数：

创建函数：使用def语句

举例：定义一个返回斐波那楔数列列表的函数

def fibs(num):    result = [0,1]    for i in range(num-2):        result.append(result[-2]+result[-1])    print(result)fibs(10)

>>>
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
>>>

文档化函数：对函数进行说明，写在函数开头的字符串，它会作为函数的一部分进行存储，称为文档字符串。

举例：给square()函数进行注释

def square(x):    ‘‘‘calculates the square of the nmber x‘‘‘    return x*x
#使用此方法访问：>>> square.__doc__‘calculates the square of the nmber x‘>>> 

return语句：函数的返回值，起到结束函数的作用，不需要返回时，返回为None

举例：

def test():    print(‘pass‘)    return    print(‘nothing‘)x = test()print(x)>>> passNone>>> 

参数：

形参：函数名后面的变量通常叫做函数的形参；

实参：调用函数时提供的值称为实参；

说明：在函数内为参数赋值新值不会改变外部任何变量的值；

举例：

#不可变参数：字符串、数字和元组def change(n):    n = ‘zyj‘    print(n)    name = ‘sl‘change(name)print(name)>>> zyjsl>>>#可变参数如列表def change(n):n[0] = ‘zyj‘print(n[0])name = [‘sl‘,‘xm‘]change(name)print(name)>>> zyj[‘zyj‘, ‘xm‘]>>># 保留原始变量的办法：def change(n):n[0] = ‘zyj‘print(n[0])name = [‘sl‘,‘xm‘]change(name[:])print(name)zyj[‘sl‘, ‘xm‘]>>>

使用函数改变数据结构的实现举例

要求：编写一个存储名字，并且能根据条件查找对应的名字

实现：定义数据结构类型为字典，通过键值（first，second）查找对应的name。

def init(data):    ‘‘‘初始化数据结构的函数‘‘‘    data[‘first‘] = {}    data[‘second‘] = {}def lookup(data,lable,name):    ‘‘‘查找人名相同函数‘‘‘    return data[lable].get(name)def store(data,full_name):    ‘‘‘将输入名字存储在数据库中函数‘‘‘    names = full_name.split()    if len(names) == 1:        names.insert(1, ‘‘)    labels = ‘first‘,‘second‘    for label,name in zip(labels,names):        peole = lookup(data,label,name)        if peole:            peole.append(full_name)        else:            data[label][name]=[full_name]>>> storage = {}>>> init(storage)>>> storage{‘first‘: {}, ‘second‘: {}}>>> store(storage, ‘zhao yujiao‘)>>> lookup(storage,‘second‘,‘yujiao‘)[‘zhao yujiao‘]>>> store(storage, ‘zhao qiaojiao‘)>>> lookup(storage,‘second‘,‘yujiao‘)[‘zhao yujiao‘]>>> storage{‘first‘: {‘zhao‘: [‘zhao yujiao‘, ‘zhao qiaojiao‘]}, ‘second‘: {‘yujiao‘: [‘zhao yujiao‘], ‘qiaojiao‘: [‘zhao qiaojiao‘]}}>>> lookup(storage,‘first‘,‘yujiao‘)>>> lookup(storage,‘first‘,‘zhao‘)[‘zhao yujiao‘, ‘zhao qiaojiao‘]>>> store(storage, ‘song qiaojiao‘)>>> storage{‘first‘: {‘zhao‘: [‘zhao yujiao‘, ‘zhao qiaojiao‘], ‘song‘: [‘song qiaojiao‘]}, ‘second‘: {‘yujiao‘: [‘zhao yujiao‘], ‘qiaojiao‘: [‘zhao qiaojiao‘, ‘song qiaojiao‘]}}>>> lookup(storage,‘second‘,‘qiaojiao‘)[‘zhao qiaojiao‘, ‘song qiaojiao‘]>>> store(storage, ‘qiaojiao‘)>>> storage{‘first‘: {‘zhao‘: [‘zhao yujiao‘, ‘zhao qiaojiao‘], ‘qiaojiao‘: [‘qiaojiao‘], ‘song‘: [‘song qiaojiao‘]}, ‘second‘: {‘‘: [‘qiaojiao‘], ‘yujiao‘: [‘zhao yujiao‘], ‘qiaojiao‘: [‘zhao qiaojiao‘, ‘song qiaojiao‘]}}

关键字参数：可以明确每个参数的作用，不需要在乎参数的位置。

def hello_1(greeting,name):    print("%s,%s!" % (greeting,name))def hello_2(name,greeting):    print("%s,%s!" % (name,greeting))hello_1("Hello","World")hello_1(greeting="Hello",name="World")>>> Hello,World!Hello,World!>>>

关键字参数可以在函数中给参数提供默认值，此时调用的时候可以不用提供参数，提供一些或提供所有参数

def hello_3(greeting="Hello",name="World"):    print("%s,%s!" % (greeting,name))hello_3()hello_3("greetings")hello_3("greetings",‘zyj‘)hello_3(name=‘zyj‘)>>> Hello,World!greetings,World!greetings,zyj!Hello,zyj!>>> 

位置参数和关键字参数结合使用

def hello_3(name,greeting="Hello",p=‘!‘):    print("%s,%s%s" % (greeting,name,p))hello_3("zyj")hello_3("zyj",p=‘!!!‘)hello_3(name=‘zyj‘)>>> Hello,zyj!Hello,zyj!!!Hello,zyj!>>> 

收集参数：参数前加星号将所有值放置在同一个元组中。一个参数里面传递多个值。

def print_params(*params):    print(params)print_params(‘zyj‘)print_params(1,2,3)print_params([1],[2],[3])print_params((1,2),(2,3))def print_params(title,*params):    print(title)    print(params)print_params(‘name:‘,‘zyj‘,‘sl‘,‘sb‘)print_params(‘name:‘)>>> (‘zyj‘,)(1, 2, 3)([1], [2], [3])((1, 2), (2, 3))name:(‘zyj‘, ‘sl‘, ‘sb‘)name:()>>> 

收集关键字参数：使用**，返回的是字典

def print_params(**params):    print(params)print_params(x=1,y=2,z=3)print_params(x=[1],y=[2],z=[3])print_params(x=(1,2),y=(2,3))def print_params(x,y,z=9,*params,**key):    print(x,y,z)    print(params)    print(key)print_params(1,2,3,4,5,6,foo=1,bar=2)print_params(1,2)>>> {‘x‘: 1, ‘y‘: 2, ‘z‘: 3}{‘x‘: [1], ‘y‘: [2], ‘z‘: [3]}{‘x‘: (1, 2), ‘y‘: (2, 3)}1 2 3(4, 5, 6){‘foo‘: 1, ‘bar‘: 2}1 2 9(){}>>> 

python函数