V. function

1. Function Definition

The function blocks of code that is packaged into a particular container, the container only needs to use the specific function, which will run through the internal code of the function call.

def fun(参数):
    函数块
    return 返回值

1.1 Katachisan

Defined parameters of the function.

Positional parameters

def fun(name, age, num):
    pass

Keyword arguments

def fun(name = 'aaron', age = 20, num = '201620'):
    pass

note

When the positional parameters and keyword parameters mix, location parameters must be before the keyword arguments.

def fun(name, age, num = '201620'):
    pass

For the default value of the function used with caution variable types.

# 如果想要给value设置默认值是空列表

# 不推荐
# 因为在建立函数时, 就已经创建了一个空列表. 在调用函数时, 若不传递value参数, 则调用的函数执行时, value指向同一个地址。
def func(data, value = []):
    pass

# 推荐
def func(data, value = None):
    if not None:
        value = []

example

# 方法一
def func(data, value = []):
    value.append(data)
    return value

v = func(1)
v1 = func(1,[11,22,33])
print(v)
v2 = func(2)
print(v,v1,v2)

# 输出结果
[1]
[1, 2] [11, 22, 33, 1] [1, 2]

# 方法二
def func(data, value = None):
    if not value:
        value = []
    value.append(data)
    return value

v = func(1)
v1 = func(1,[11,22,33])
print(v)
v2 = func(2)
print(v,v1,v2)

#输出结果
[1]
[1] [11, 22, 33, 1] [2]

Special parameter

def func(*args, **kwargs):
    pass

# 其中*args用来接受除字典以外的其他类型的参数, **kwargs用来接受字典类型的参数

1.2 argument

When you call the function, passing the parameters.

def fun(name, age, num):
    pass
fun('aaron', 20, '201620')

note

Parameter transfer function memory address (reference).

1.3 Return Values

Who calls a function, the return value of a function assigned to it who, when not specify a return value, default return None.

def fun(name, age, num):
    return name, age, num

note
- Function is not called, the internal function statement will not be executed !!!
- Each time a function call, the call will be to open up a memory, the memory can hold the value of their future want to use.

2. anonymous function

definition

The so-called anonymous function is not the function of the function name, but with the lambda keyword to define.

lambda x, y: x + y

The above formulas are functionally equivalent to the following function.

def fun(x, y):
    return x + y

3. recursive function

Function calls itself

def recursion():
    num = input('请输入一个阿拉伯数字:')
    if num.isdecimal():
        print('输入成功')
    else:
        print('\n输入错误! 重新开始!\n')
        recursion() # 在此处调用了自己

recursion()

4. Closure

definition

Create an area for the function (internal variables for their own use), providing data for it later execution.

name = 'oldboy'
def bar(name):
    def inner():
        print(name)
    return inner
v1 = bar('alex') # {name = alex, inner} # 闭包
v2 = bar('eric')
v1()
v2()

example

Example 1

name = 'alex'
def base():
    print(name)

def func():
    name = 'eric'
    base()   
func()

# 输出结果为
alex

Example 2

info = []

def func(i):
    def inner():
        print(i)
    return inner

for item in range(10):
    info.append(func(item))

info[0]()
info[1]()
info[4]()

# 输出结果为
0
1
4

Example 3

name ='aaron'
def fun():
    def inner():
        print(name)
    return inner() # 相当于 v = inner();return v  inner无返回值,所以v = None, 调用fun()的返回值就为None
    # return inner # 若语句为左边所示,则最后的输出结果为inner函数所在的内存地址
r = fun()
print(r)