多类型传值和冗余参数

1. 多类型传参

In [1]: def fun(x, y):
   ...:     return x + y
   ...:

In [2]: fun(1, 5)
Out[2]: 6

In [3]: t = (1, 5)

In [4]: fun(t)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-21f7b4b850d7> in <module>()
----> 1 fun(t)

TypeError: fun() takes exactly 2 arguments (1 given)

In [5]: fun(*t)
Out[5]: 6

In [6]: w = [1, 5]

In [7]: fun(*w)
Out[7]: 6

In [8]: def sum(x, y, z):
   ...:     return x + y + z
   ...:

In [9]: sum(10, *t)
Out[9]: 16

In [10]: sum(10, *w)
Out[10]: 16

In [11]: sum(*t, 10)
  File "<ipython-input-11-ccfcd859f3aa>", line 1
    sum(*t, 10)
SyntaxError: only named arguments may follow *expression


In [12]: sum(*(10, 1, 5))
Out[12]: 16

In [13]: sum(*[10, 1, 5])
Out[13]: 16

In [20]: dic = {'x':1, 'y':3, 'z':5}

In [21]: sum(**dic)
Out[21]: 9

2. 冗余参数

• 向函数传元组和字典
• 处理多余实参
• def fun(x, y, *args, **kwargs)

In [15]: def fun(x, *args, **kwargs):
    ...:     print x
    ...:     print args
    ...:     print kwargs
    ...:

In [16]: fun()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-16-d9f830ba61f1> in <module>()
----> 1 fun()

TypeError: fun() takes at least 1 argument (0 given)

In [17]: fun(3)
3
()
{}

In [18]: fun('a')
a
()
{}

In [27]: fun('a', 2, ['b', 3])
a
(2, ['b', 3])
{}

In [28]: fun([1, 2], 'a', 2, ['b', 3])
[1, 2]
('a', 2, ['b', 3])
{}

In [29]: dic
Out[29]: {'x': 1, 'y': 3, 'z': 5}

In [30]: fun(dic, ['a', ('b', 3), 5], ('x', 2), 9)
{'y': 3, 'x': 1, 'z': 5}
(['a', ('b', 3), 5], ('x', 2), 9)
{}

In [31]: dic2 = {'a':6, 'b':7, 'c':8}

In [32]: fun(dic, dic2)
{'y': 3, 'x': 1, 'z': 5}
({'a': 6, 'c': 8, 'b': 7},)
{}

In [39]: fun(dic, **dic2)
{'y': 3, 'x': 1, 'z': 5}
()
{'a': 6, 'c': 8, 'b': 7}

In [42]: fun(dic, dic, *t, *w, **dic2)
  File "<ipython-input-42-ea2cb6c1864b>", line 1
    fun(dic, dic, *t, *w, **dic2)
                      ^
SyntaxError: invalid syntax


In [43]: fun(dic, dic, *t, **dic2)
{'y': 3, 'x': 1, 'z': 5}
({'y': 3, 'x': 1, 'z': 5}, 1, 5)
{'a': 6, 'c': 8, 'b': 7}

In [44]: fun(1, 'a', [1, 2], *t, g=6, j=8, **dic2)
1
('a', [1, 2], 1, 5)
{'a': 6, 'c': 8, 'b': 7, 'g': 6, 'j': 8}

函数的递归调用

• 必须有最后的默认结果，如 if n == 0
• 递归参数必须向默认结果收敛，如 factorial(n-1)

# 1) 使用循环实现阶乘函数

In [45]: def factorial(n):
    ...:     f = 1
    ...:     for i in range(1, n+1):
    ...:         f *= i
    ...:     return f
    ...:

In [46]: factorial(4)
Out[46]: 24

# 2) 使用递归实现阶乘函数

In [47]: def factorial(n):
    ...:     if n == 0:
    ...:         return 1
    ...:     else:
    ...:         return n * factorial(n-1)
    ...:

In [48]: factorial(4)
Out[48]: 24