python函数参数、参数解构、作用域、递归及匿名函数

    def add(*nums)
        >>> def add(*nums):
        sum = 0
        print(type(nums))
        for x in nums:
            sum += x
        print(sum)
        >>> add(3,6,9)
        <class ‘tuple‘>
        18

>>> def show(**kwargs):
        for k,v in kwargs.items():
            print(‘{}={}‘.format(k,v))
        >>> show(a=1,b=2,c=3)
        a=1
        c=3
        b=2

    >>> def fn(x,y,*args,**kwargs):
            print(x)
            print(y)
            print(args)
            print(kwargs)
    
        >>> fn(3,5,6,9,10,a=1,b=‘python‘)
        3
        5
        (6, 9, 10)
        {‘a‘: 1, ‘b‘: ‘python‘}
        >>> fn(3,5)
        3
        5
        ()
        {}
        >>> fn(3,5,a=1,b=‘python‘)
        3
        5
        ()
        {‘a‘: 1, ‘b‘: ‘python‘}
        >>> 

    >>> def fn(*args,x):
            print(x)
            print(args)
    >>> fn(3,5)  调用报错
    >>> fn(3,5,x=7)    
    args已经截获了所有的位置参数，x不使用关键字参数就不可能拿到实参
    
    >>> def fn(*kwargs,x):
            print(x)
            print(args)
    直接报语法错误，因为kwargs会截获所有的关键字参数

>>> def fn(x,y,z=3,*args,m=4,n,**kwargs):
            print(x,y,z,m,n)
            print(args)
            print(kwargs)
            
    def connect(host=‘localhost‘, port=‘3306‘, user=‘admin‘, password=‘admin‘, **kwargs):
    
    >>> def connect(host=‘localhost‘, port=‘3306‘, user=‘admin‘, password=‘admin‘, **kwargs):
        print(host,port)
        print(user,password)
        print(kwargs)
        >>> connect(db=‘cmdb‘)
        localhost 3306
        admin admin
        {‘db‘: ‘cmdb‘}
        >>> connect(host=‘192.168.1.1‘,db=‘cmdb‘)
        192.168.1.1 3306
        admin admin
        {‘db‘: ‘cmdb‘}
        >>> 

举例：
        >>> def add(x,y):
            return x+y
    
        1、位置参数解构
        >>> add(*(4,5))
        9
        >>> add(*[4,5])
        9
        >>> 
        
        2、关键字参数解构
        >>> d = {‘x‘:5,‘y‘:6}
        >>> add(**d)
        11
        >>> 

        3、参数解构和可变参数
        >>> def add(*args):
                result = 0
                for x in args:
                    result += x
                return result

        >>> add(1,2,3)
        6
        >>> add(*[1,2,4])
        7
        >>> add(*range(10))
        45
        >>> 

举例：
    x = 5
    >>> def foo():
        x += 1
        print(x)
    >>> foo()
    x += 1其实是x = x+1,相当于在foo内部定义一个局部变量x，那么foo内部所有x都是这个局部变量
    但是这个x还没有完成赋值，就被右边拿来使用了，导致报错 
    
    使用全局变量global关键字变量，将foo内的x声明为使用外部的全局作用域中定义的x
    全局作用域中必须要有x的定义
    
    >>> def foo():
            global x
            x = 10
            x += 1 #x在内部作用域为一个外部作用域的变量赋值，所以x += 1不会报错
            print(x)
    >>> foo()

斐波那契数列Fibonacci number：1,1,2,3,5,8,13,21,34,55.....
如果设F（n）为该数列的第n项,那么这句话可以写成如下形式：F(n)=F(n-1)+F(n-2)
F(0)=0,F(1)=1,F(n)=F(n-1)+F(n-2)

pre = 0
cur = 1
print(pre,cur,end=‘‘)
n = 4
for i in range(n-1):
    pre,cur = cur,pre+cur
    print(cur,end=‘‘)

解析：
fib(3)+fib(2)
fib(3)调用fib(3),fib(2),fib(1)

递归举例：
import datetime

n = 35
start = datetime.datetime.now()

def fib(n):
    return 1 if n<2 else fib(n-1) + fib(n-2)

for i in range(n):
    print(fib(i),end=‘‘)
delta = (datetime.datetime.now() - start).total_seconds()
print(delta)


改下后:
pre = 0
cur = 1

print(pre,cur.end=‘‘)
def fib(n,pre=0,cur=1):
    pre,cur = cur, pre+cur
    print(cur,end=‘‘)
    if n == 2:
        return
    fib(n-1,pre,cur)
fib(n)

举例：
        >>> print((lambda :0)())
        0
        >>> print((lambda x,y=3:x+y)(5))
        8
        >>> print((lambda x,*,y=30:x+y)(5))
        35
        >>> print((lambda x,*,y=30:x+y)(5,y=10))
        15
        >>> print((lambda *args:(x for x in args))(*range(5)))
        <generator object <lambda>.<locals>.<genexpr> at 0x0000000003074258>