2019.08.09 learning finishing

Function object

Functions are first-class objects, i.e. function may be used as the data processing.

1. The four functions of the function object

1. references

x = 'hello nick'
y = x

f = func
print(f)

<function func at 0x10af72f28>

2. as a parameter passed to a function

len(x)


def foo(m):
    m()


foo(func)
from func

3. The return value can be used as a function of

def foo(x):
    return x


res = foo(func)
print(res)
res()

<function func at 0x10af72f28>

from func

4. The types of elements can be used as a container

l = [x]

function_list = [func]
function_list[0]()

from func

Nested functions

1. function nested definitions

Internal function defined functions can not be used inside a function defined in an external function.

def f1():
    def f2():
        print('from f2')
    f2()
f1()

from f2

2. nested function calls

def max2(x, y):
    if x > y:
        return x
    else:
        return y


def max4(a, b, c, d):
    res1 = max2(a, b)
    res2 = max2(res1, c)
    res3 = max2(res2, d)
    return res3


print(max4(1, 2, 3, 4))

Namespace and scope

1. Name Space

Namespace (name spaces): In the memory management when that chapter, we said that to create a variable is actually opened up a new space in memory. But we've been avoiding storing variable names, in fact, there is room for a binding relationship between a variable name and variable memory storage in memory, and this space is called a namespace.

1.1 built-in namespace

Built-in namespace: Store Pyhton interpreter that comes with the name, such asint、float、len

Life cycle: when the interpreter started to take effect, fail when the interpreter is closed

1.2 global name space

Global namespace: In addition to the built-in and a local name, the rest are stored in the global namespace, such as the following codex、func、l、z

Life cycle: when the file is executed into effect, expire after file execution

x = 1

def func():
    pass

l = [1, 2]

if 3 > 2:
    if 4 > 3:
        z = 3

1.3 The local name space

The local name space: the name of the function body for storing generated during a function call, such as the following codef2

Life Cycle: take effect during the function call when the file is executed, expire after the function execution

def f1():
    def f2():
        print('from f2')
    f2()

f1()

2. Scope

Domain refers to a region, i.e. the region scope of action.

Global Scope: Global effective, global survival, and includes built-in namespace global name space.

2.1 global scope

# 全局作用域
x = 1


def bar():
    print(x)


bar()
1

2.2 local scope

# 局部作用域
def f1():
    def f2():
        def f3():
            print(x)
        x = 2
        f3()
    f2()


f1()
2

2.3 Notes

# 作用域注意点
x = 1


def f1():  # 定义阶段x=1
    print(x)


def f2():
    x = 2
    f1()


f2()
1

2.4 Application of scopes function object +

# 作用域应用
def f1():
    def inner():
        print('from inner')
    return inner


f = f1()  # 把局部定义的函数放在全局之中


def bar():
    f()


bar()
from inner