python——函数

函数

python也分形参实参

函数文档（突然发现tab是好用的）

 def myfirstfun(name):'xxxx'#xxxxxprint(name)>>> myfirstfun(x）   SyntaxError: invalid character in identifier>>> myfirstfun('x')x>>> myfirstfun.__doc__'xxxx'>>> help(myfirstfun)Help on function myfirstfun in module __main__:myfirstfun(name)    xxxx>>> print.__doc__"print(value, ..., sep=' ', end='\\n', file=sys.stdout, flush=False)\n\nPrints the values to a stream, or to sys.stdout by default.\nOptional keyword arguments:\nfile:  a file-like object (stream); defaults to the current sys.stdout.\nsep:   string inserted between values, default a space.\nend:   string appended after the last value, default a newline.\nflush: whether to forcibly flush the stream.">>> help(print)Help on built-in function print in module builtins:print(...)    print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)        Prints the values to a stream, or to sys.stdout by default.    Optional keyword arguments:    file:  a file-like object (stream); defaults to the current sys.stdout.    sep:   string inserted between values, default a space.    end:   string appended after the last value, default a newline.    flush: whether to forcibly flush the stream.

>>> 

关键字参数

>>> tell('misszhou','让编程编织梦想')misszhou让编程编织梦想>>> tell(wors='words',name='misszhou')Traceback (most recent call last):  File "<pyshell#16>", line 1, in <module>    tell(wors='words',name='misszhou')TypeError: tell() got an unexpected keyword argument 'wors'>>> tell(words='words',name='misszhou')misszhouwords

默认参数

>>> def saysome(name='name',word='word'):print(name+word)>>> saysome<function saysome at 0x000000A74A7969D8>>>> saysome()nameword

收集参数（这玩意别的语言没有，类C语言有可变参数啊）print的实现

>>> def test(*par):print('len',len(par))print(par[0])>>> test(1,2,3,4)len 41>>> def test(*par,exp=8)SyntaxError: invalid syntax>>> def test(*par,exp=8):print('len:',len(par),exp)print('第二个参数为',par[1])>>> test(1,2,3,4)len: 4 8

第二个参数为 2

函数与过程

python可以返回多个值（通过列表打包呗）

>>> def back():return 1,'misszhou'>>> back()(1, 'misszhou')

python也分全局变量/局部变量

一段神奇的代码

def discount(price,rate):    fin_price=price*rate    # print('这里试图打印全局变量old_price:',old_price)    old_price=50    print('1修改后oldprice的值',old_price)    return fin_priceold_price=float(input('请输入原价:'))rate=float(input('请输入折扣;'))new_price=discount(old_price,rate)print('2修改后oldprice的值',old_price)print('折扣后价格:',new_price)请输入原价:100请输入折扣;0.91修改后oldprice的值 502修改后oldprice的值 100.0折扣后价格: 90.0

为什么呢？在函数里面的那个是新创建的局部变量！！不是原来的那个全局变量

我要是想在函数里面修改全局变量，也可以嵌套定义

内嵌函数和闭包

global关键字（这玩意和php一样啊=w=）

>>> count=5>>> def myfun()SyntaxError: invalid syntax>>> def myfun():count=10print(count)>>> def myfun()SyntaxError: invalid syntax>>> myfun()10>>> print(count)5>>> def myfun():global countcount=10print(10）      SyntaxError: invalid character in identifier>>> def myfun():global countcount=10print(10)>>> def myfun():global countcount=10print(count)>>> def myfun()SyntaxError: invalid syntax>>> myfun()10>>> print(count)10

函数嵌套

>>> def fun1():print('fun1')def fun2():print('fun2')fun2()>>> fun1()fun1fun2>>> fun2()Traceback (most recent call last):  File "<pyshell#68>", line 1, in <module>    fun2()NameError: name 'fun2' is not defined>>> fun1().fun2()fun1fun2Traceback (most recent call last):  File "<pyshell#69>", line 1, in <module>    fun1().fun2()AttributeError: 'NoneType' object has no attribute 'fun2'闭包（这玩意js有啊）>>> def funx(x):def funy(y):return x*yreturn funy>>> i=funx(8)>>> i<function funx.<locals>.funy at 0x0000004A51346A60>>>> type(i)<class 'function'>>>> i(5)40>>> funx(4)(4)16>>> funy(8)Traceback (most recent call last):  File "<pyshell#80>", line 1, in <module>    funy(8)NameError: name 'funy' is not defined>>> def fun1():x=5def fun2():x*=xreturn xreturn fun2()>>> fun1()Traceback (most recent call last):  File "<pyshell#88>", line 1, in <module>    fun1()  File "<pyshell#87>", line 6, in fun1    return fun2()  File "<pyshell#87>", line 4, in fun2    x*=xUnboundLocalError: local variable 'x' referenced before assignment>>> def fun1():x[0]=5def fun2():x[0]*=x[0]return x[0]return fun2()>>> fun1()Traceback (most recent call last):  File "<pyshell#91>", line 1, in <module>    fun1()  File "<pyshell#90>", line 2, in fun1    x[0]=5NameError: name 'x' is not defined>>> def fun1():x=[5]def fun2():x[0]*=x[0]return x[0]return fun2()>>> fun1()25>>> def fun1():x=5def fun2():nonlocal xx*=xreturn xreturn fun2()>>> fun1()25

lambda表达式

参数：返回值

>>> x=lambda x,y:x+y>>> print(x)<function <lambda> at 0x0000004A51346EA0>>>> x(3,4)7

这玩意在js里面不也有么……

lambda表达式的作用

省下定义函数的作用、不需要考虑函数名、省得函数阅读跳到开头定义部分

filter()过滤器

help(filter)Help on class filter in module builtins:class filter(object) |  filter(function or None, iterable) --> filter object |   |  Return an iterator yielding those items of iterable for which function(item) |  is true. If function is None, return the items that are true. |   |  Methods defined here: |   |  __getattribute__(self, name, /) |      Return getattr(self, name). |   |  __iter__(self, /) |      Implement iter(self). |   |  __new__(*args, **kwargs) from builtins.type |      Create and return a new object.  See help(type) for accurate signature. |   |  __next__(self, /) |      Implement next(self). |   |  __reduce__(...)<pre name="code" class="python">>>> def odd(x):return x%2>>> temp=range(10)>>> show=filter(odd,temp)>>> list(show)[1, 3, 5, 7, 9]

| Return state information for pickling.filter(None,[1,0,False,True])<filter object at 0x0000004A5135B240>>>> list(filter(None,[1,0,False,True]))

[1, True]

默认把一切非正的过滤掉

自定义：

>>> def odd(x):return x%2>>> temp=range(10)>>> show=filter(odd,temp)>>> list(show)[1, 3, 5, 7, 9]

学以致用精简一下

>>> list(filter(lambda x:x%2,range(10)))

map()

映射

list(map(lambda x:x%2,range(10)))[0, 1, 0, 1, 0, 1, 0, 1, 0, 1]

递归

可以人为规定递归层数

import syssys.setrecursionlimit(10000)

输出阶乘

def func(num):    if(num==1):        return 1    return num*func(num-1)num=int(input())print(func(num))

递归的斐波那契

def fun(n):    if(n==3):        return 2    elif(n==2):        return 1    return fun(n-1)+fun(n-2)print(fun(12))

汉诺塔

def hano(n,x,y,z):    if(n==1):        print(x,"-->",z)        return    hano(n-1,x,z,y)    print(x,"-->",z)    hano(n-1,y,x,z)n=int(input())hano(n,'x','y','z')