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This article introduces the relevant knowledge of "how to understand python function objects and closures". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

1. Function object

In Python, everything is an object, and functions are no exception. Functions as objects can be assigned to a variable, can be added to a collection object as elements, can be passed to other functions as parameter values, and can also be used as return values of functions. These properties are unique to the first kind of objects.

1. Functions can be referenced

> def add (xQuery):

... Return Xeroy

...

> func=add

> func (1Pol 2)

three

2. The function can be used as an element of container type

> dic= {'add':add,'max':max}

> dic

{'add':,' max':}

> dic ['add'] (1 ~ 2)

three

3. A function can be passed into another function as an argument

> def foo (xQuery yrefunc):

... Return func (XBI y)

...

> foo (1, 2, 2, add)

three

4. The return value of a function can be a function

Def bar ():

Return add

Func=bar ()

Func (1 dint 2)

three

5. Application cases

(1) the simplest way to write

Def login ():

'' login''

Print ('login successful')

Def registry ():

'Register'

Print ('registered successfully')

Def check_balance ():

'' query balance''

Print ('balance query succeeded')

Def withdraw ():

'withdraw cash'

Print ('withdrawal successful')

Print (''

1 login

2 Registration

3 query balance

4 withdraw cash

'')

Choice = input ('Please enter the operation number you want to perform:') .strip ()

If choice = = '1mm:

Login ()

Elif choice = = '2percent:

Registry ()

Elif choice = = '3percent:

Check_balance ()

Else:

Withdraw ()

Disadvantages: if there are many functions, then the redundancy is too large, and it is not convenient to add functions later.

(2) optimized code

Def login ():

'' login''

Print ('login successful')

Def registry ():

'Register'

Print ('registered successfully')

Def check_balance ():

'' query balance''

Print ('balance query succeeded')

Def withdraw ():

'withdraw cash'

Print ('withdrawal successful')

Func = {

'0quit: (' exit', None)

'1login: ('login', login)

'2register: ('register', registry)

'3percent: ('query balance', check_balance)

'4percent: ('withdrawal', withdraw)

}

While True:

For i in func:

Print (iPaper func [I] [0])

Choice = input ('Please enter the operation number you want to perform:') .strip ()

If choice = = '0mm:

Break

Elif choice not in func:

Print ('Hello, dear users! The operation you need to perform does not exist, please reselect the operation number!')

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Else:

Func [choice] [1] ()

Second, function nesting

A new function is defined in the function body of another function. Call it function nesting.

1. Application case 1

We put all the operation functions of the circle into the circle function to determine which function to call and which operation to perform by specifying the value of the action parameter (similar to the specified rfield wpenery a mode in file processing).

2. Closure function

(1) closure and package

When a function is treated as data, it always follows the local scope. If the embedded function contains references to variables in the scope of the external function (rather than the global scope), then the 'embedded function' is a Closures function, or closure for short.

Xero1

Def outer ():

Xerox 2

Def inner ():

Print (x) # where x is the variable x of the external function, so inner is a closure function

Return inner

Func=outer ()

Func () # result is 2

You can view the external variables wrapped by the closure function through the closure property of the function

> func.__closure__

()

> func.__closure__ [0] .cell _ contents

two

"closed" represents that the function is internal, and "package" represents the reference to the outer scope of the function. So no matter where the closure function is called, the variables that are wrapped around it are still used.

3. The use of closure function

So far, we have got two ways to pass a value for the body of a function, one is to pass the value directly as a parameter, and the other is to pass the value indirectly to the closure function.

Import requests

# method 1:

Def get (url):

Return requests.get (url). Text

# method 2:

Def page (url):

Def get ():

Return requests.get (url) .text # url is a variable of an external function, so get is a closure function

Return get

Tip: the requests module is used to simulate the browser to send a request to the website and download the page content locally, which needs to be installed in advance: pip3 install requests

Comparing the two methods, method one needs to pass in url repeatedly when downloading the same page, while method two only needs to pass a value once to get a closure function containing the specified url. There is no need to pass url to call the closure function later.

……

This property of closure functions is sometimes called lazy computing. Using the method of wrapping values to functions will also be useful in the next decorator.

So much for the introduction of "how to understand python function objects and closures". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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