def func(a, b):
  print(a+b)

func(1, 2) #3

def power(x, n):
  s = 1
  while(n > 0):
    n -= 1
    s *= n
  return s

power(2, 3) #8

def power(x, n=2):
  s = 1
  while(n > 0):
    n -= 1
    s *= n
  reutrn s

power(3)  #9
power(2, 3) #8

#以下这个函数如果被多次调用会在默认添加多个END字符串
def add_end(l = []):
  l.append('END')
  return l

#为了避免这个问题，应该把传入的默认参数设置为不可变的
def add_end(l = None):
  l = []
  l.append('END')
  return l

#这才是可变参数，虽然在使用上和列表没有区别，但是参数nums接收到的是一个tuple（这些参数在传入时被自动组组装为一个元祖）
def calc(*nums):
  sum = 0
  for n in nums:
    sum += n
  return sum

> calc(1,2,3)
7

> my_ls = [1,2,3]
> calc(*my_ls)
7

#用两个星号表示关键字参数
def person_info(name, age, **kw):
  print("name", name, "age", age, "other", kw)

> person_info("Xiaoming", 12)
name Xiaoming age 12 other{}
> person_info("Dahuang", 35, city = "Beijing")
name Dahuang age 35 other {'city':'Beijing'}

#这里星号分割符后面的city、job是命名关键字参数
person_info(name, age, *, city, job):
  print(name, age, city, job)

> person_info("Alex", 17, city = "Beijing", job = "Engineer")
Alex 17 Beijing Engineer  #看来这里不再被自动组装为字典

#args是变长参数，而city和job是命名关键字参数
person_info(name, age, *args, city, job):
  print(name, age, args, city)

> person_info("Liqiang", 43, "balabala", city = "Wuhan", job = "Coder")
Liqiang 43 balabala Wuhan Coder

def f1(a, b, c=0, *args, **kw):
  print("a = ", a, "b = ", b, "args = ", args, "kw = ",kw)
def f2(a, b, c=0, *, d, **kw):
  print("a = ", a, "b = ", b, "c = ", c, "d = ", d, "kw = ", kw)

> f1(1, 2)
a = 1 b = 2 c = 0 args =() kw = {}
> f1(1, 2, c=3)
a = 1 b = 2 c = 3 args = () kw = {}
> f1(1, 2, 3, 'a', 'b')
a = 1 b = 2 c = 3 args = ('a', 'b') kw = {}
> f1(1, 2, 3, 'a', 'b', x = 99)
a = 1 b = 2 c = 3 args = ('a', 'b') kw = {'x':99}
> f2(1, 2, d = 99, ext = None)
a = 1 b =2 c = 0 d = 99 kw = {'ext':None}