Python基础笔记：函数：调用函数、定义函数、函数的参数、递归函数

#Sublime Text
import math
def ee(a,b,c):
    delta=b*b-4*a*c
    if delta<0:
        return ‘null‘
    else:
        m=math.sqrt(delta)
        nx=(-b+m)/2/a
        ny=(-b-m)/2/a
        return nx,ny

#python解释器
>>> from hello import ee  #声明调用py文件中所定义的函数ee
>>> ee(1,0,9)
‘null‘
>>> ee(1,0,-9)
(3.0, -3.0)

def pow(x):  
    return x*x  #求x的平方
    
def pow(x,n):
    if n==0:
        return 1
    if n==1:
        return x
    return x*pow(x,n-1)  #求x的任意次方

#默认求x平方
def pow(x,n=2):
    if n==0:
        return 1
    if n==1:
        return x
    return x*pow(x,n-1)

>>> from hello import pow
>>> pow(5)
25
>>> pow(5,3)
125
>>> pow(5,0)
1

#幼儿园新生等级，默认新生年龄为6，城市为ZZ
def sign_in(name,gender,Age=6,city=‘ZZ‘):
    print(name,gender,Age,city)

>>> sign_in(‘jiaxinwei‘,‘boy‘)
jiaxinwei boy 6 ZZ
>>> sign_in(‘jiaxinwei‘,‘boy‘,city=‘NY‘)
jiaxinwei boy 6 NY

def calc(*nums):
    sum=0
    for n in nums:
        sum=sum+n*n
    return sum

>>> a=[1,2,3,4]
>>> calc(*a)
30
>>> calc(1,2,3,4)
30
>>> calc(a)

def person(name,age,**kw):
    print(‘name:‘,name,‘age:‘,age,‘other:‘,kw)
#其中name,age是必选参数，kw是关键字参数。在调用该函数时，可以只传入必选参数，也可以传入任意个关键字参数，关键字参数在函数内部自动组装为一个dict。

>>> from hello import person
>>> person(‘jiaxinwei‘,8) #1
name: jiaxinwei age: 8 other: {}
>>> person(‘jiaxinwei‘,8,city=‘NY‘,gender=‘M‘) #2
name: jiaxinwei age: 8 other: {‘city‘: ‘NY‘, ‘gender‘: ‘M‘}
>>> extra={‘city‘:‘Beijing‘,‘job‘:‘Student‘} #3
>>> person(‘jack‘,24,**extra)
name: jack age: 24 other: {‘city‘: ‘Beijing‘, ‘job‘: ‘Student‘}

def person(name, age, *, city, job):
    print(name, age, city, job)
# *号前面的是必选参数，后面的是命名关键字参数

#如果函数定义中已经有了一个可变参数，后面跟着的命名关键字参数就不再需要一个分隔符了
def person(name,age,*args,city,job):
    print(name,age,args,city,job)

#命名关键字函数可以有缺省值
def person(name,age,*,city=‘Beijing‘,job=‘student‘):
    print(name,age,city,job)

>>> from hello import person
>>> person(‘jiaxinwei‘,11)
jiaxinwei 11 Beijing student

def product(*nums):
    if len(nums)==0:
        sum=0
    else:
        sum=1
    for x in nums:
        sum*=x
    return sum

>>> from hello import product
>>> product()
0
>>> product(5)
5
>>> product(5,6,7)
210
>>> product(5,6,7,9)
1890