Python Learning: Function advanced

Highlights of this section: Namespaces and scopes, function nesting, function name essence, closures

Namespaces:

The nature of a namespace: a binding relationship between a name and a value.

Three types of namespaces:

Global namespaces

Local namespaces

Built-in namespaces

Order of loading and taking values between three namespaces:

Load order: Built-in namespaces (pre-Program load)-Global namespaces (program run: Load from top to bottom) local namespaces (program run: Load only when called)

Value:

Built-in namespaces, local namespaces, and global namespaces, local call spaces

Global invocation: Built-in namespaces, global namespaces

Scope:

Scope is the scope of action, according to the effective scope can be divided into global scope and local scope.

Global scope: Contains a built-in namespace, a global namespace, and can be referenced and globally valid anywhere in the entire file.

Local scope: Local namespace, which can only take effect within a local scope.

Globals and locals one is global, one is local.

Nested calls to functions:

　　

def max2 (x, y    )  : Mifelse  y    return  mdef  max4 (a,b,c,d):    = max2 (A,    b)= max2 (    res1,c)= Max2 (res2, d)    return  res3#  max4 (23,-7,31,11)

nested calls to functions

def F1 ():     Print ("inF1")     def F2 ():         Print ("inF2")    F2 () F1 ()

nested definitions of functions (i)

def F1 ():     def F2 ():         def f3 ():             Print ("inf3")         Print ("inF2")        f3 ()    print("inF1  ")    F2 ()    F1 ( )

nested definitions of functions (ii)

The scope chain of the function:

def F1 ():     = 1    def  F2 ():        print(a)    F2 () F1 ()

scope Chain (i)

def F1 ():     = 1    def  F2 ():        def  f3 ():            print(a)        F3 ()    F2 () F1 ( )

scope Chain (ii)

def F1 ():     = 1    def  F2 ():        = 2    f2 ()    print('  , a) F1 ()

scope Chain (iii)

nonlocal keywords

# 1. External must have this variable
# 2. Variables with the same name can no longer appear before an intrinsic function declares a nonlocal variable
# 3. Internally modify this variable if you want to take effect in the first layer function that has this variable externally

def F1 ():     = 1    def  F2 ():        nonlocal a        = 2    f2 ()    print('  ', a) F1 ()

nonlocal Keywords

The nature of the function name:

　　The essence of a function name is the memory address of the stored function

1. Can be referenced

2. Elements that can be used as container types

3. Can be used as a function parameter and return value

Small summary: Just use it as a variable.

Closures:

　An intrinsic function contains a reference to an outer scope rather than a global role name word, which is called a closure function.

def func ():     ' Eva '    def inner ():         Print (name)     return  = func () f ()

common usage of closure functions

#the __closure__ of the output has a cell element: a closure functiondeffunc (): Name='Eva'    definner ():Print(name)Print(Inner.__closure__)    returnInnerf=func () f ()#the output __closure__ is none: Not a closure functionName ='Egon'defFunc2 ():definner ():Print(name)Print(Inner.__closure__)    returnInnerf2=Func2 () f2 ( )

determine if it is a closure

def wrapper ():     = +    def  func ():        'Eva'        def  Inner ():             Print (Name,money)         return Inner     return  == f () I ()

Closure Nesting

 from Import Urlopen def index ():     " http://www.cnblogs.com/Eva-J/articles/7156261.html "    def get ():         return urlopen (URL). Read ()     return  == Xiaohua ()print(content)

get web content with closures

Closure leads to the next lesson, adorners ...

Summarize:

　Slightly

Python Learning: Function advanced