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1. Decorator 1. Related knowledge points

* args: responsible for summarizing and assigning excess location arguments to args

* * kwargs: it is responsible for summarizing and assigning excess keywords to kwargs.

Namespace and scope

Function object:

You can pass in a function as an argument

You can return the function as a return value

Nested definition of a function: define a function within a function

Closure function: the return value of the parent function is a function, the returned function calls the local variable of the parent function, and the function can be executed outside the parent function

Decorator:

Decorator: define a function that adds functionality to other functions

Why use decorators?

Open and closed principle: modification of open extended functions but closed source code

The decorator adds new functions to the decorative object without modifying the source code of the decorative object and the way it is called.

Decorator implementation:

Requirements: do not modify the source code, calculate the code execution time

Source code:

Import timedef func0 (x): time.sleep (1) print (x) func0 (0) # scenario 1: the function of calculating the code execution time is implemented, but the source code is modified Does not meet the requirements def func1 (x): start = time.time () time.sleep (1) print (x) end = time.time () print ('scenario 1 run time: {}' .format (end-start)) func1 (1) # scenario 2: meet the requirements But the code does not have reusability start = time.time () func0 (2) end = time.time () print ('scenario 2 run time: {}' .format (end-start)) # scenario 3: encapsulate scenario 2 as a function, but modify the way the function is called Does not meet the requirements def wrapper (): start = time.time () func0 (3) end = time.time () print ('scenario 3 run time: {}' .format (end-start)) wrapper () # scenario 4: do not modify the calling mode of the original function def wrapper (x): start = time.time () func0 (x) end = time.time () print ('scenario 4 runs Time: {} '.format (end-start) wrapper (4) # scenario 5: option 4 parameters are written to death Optimization scheme 4 def wrapper (* args, * * kwargs): start = time.time () func0 (* args, * * kwargs) end = time.time () print ('scheme 5 run time: {}' .format (end-start)) wrapper (5) # scenario 6: option 5 function is written dead, optimization scheme 5 But modified the method of calling the source code def outter (a): def wrapper (* args, * * kwargs): start = time.time () a (* args, * * kwargs) end = time.time () print ('scheme 6 run time: {}' .format (end-start)) return wrapperf = outter (func0) f (6) # scenario 7: optimization scheme 6 (outter is the decorator) For decorating func0) def outter (a): def wrapper (* args, * * kwargs): start = time.time () a (* args, * * kwargs) end = time.time () print ('scenario 7 run time: {}' .format (end-start)) return wrapperfunc0 = outter (func0) # steal the beam and change the column, the caller is not aware of func0 (7)

Running result:

0

one

Program 1 running time: 1.001857042312622

two

Run time of option 2: 1.0040733814239502

three

Scheme 3 running time: 1.0017154216766357

four

Program 4 running time: 1.007995367050171

five

Program 5 running time: 1.0145602226257324

six

Program 6 running time: 1.0046615600585938

seven

Run time of plan 7: 1.0094060897827148

two。 Grammatical sugar

To use grammatical sugar, you need to place the decorator in front of the decorated object.

# No syntax sugar import timedef func0 (x): time.sleep (1) print (x) # func0 (0) def outter (a): def wrapper (* args, * * kwargs): start = time.time () a (* args) * * kwargs) end = time.time () print ('run time: {}' .format (end-start)) return wrapperfunc0 = outter (func0) func0 ('hello') # use syntax sugar import timedef outter (a): def wrapper (* args, * * kwargs): start = time.time () a (* args) * * kwargs) end = time.time () print ('run time: {}' .format (end-start)) return wrapper@outter # grammatical sugar Equivalent to the line func0 = outter (func0) def func0 (x): time.sleep (1) print (x) func0 ('hello') print (func0.__name__)

Running result:

Hello

Running time: 1.0050427913665771

Wrapper

3. Decorator template # decorator template def decorator_name (x): def wrapper (* args, * kwargs): #. The newly added function. # is the format x (* args, * * kwargs) return wrapper@decorator_name def func_name (): pass for calling the original function.

Expansion: the real realization of changing beams for posts, without the perception of the caller

Do not use decorator

# No decorator import timedef func0 (x): time.sleep (1) print (x) func0 ('hello') print (func0.__name__) # View function name print (help (func0)) # View help (mainly for comments)

Running result:

Hello

Func0

Help on function func0 in module main:

Func0 (x)

This is a function.

None

Use the decorator:

Import timedef outter (a): def wrapper (* args, * * kwargs):''this is the decorator' 'start = time.time () a (* args) * * kwargs) end = time.time () print ('run time: {}' .format (end-start)) return wrapper@outter # func0 = outter (func0) def func0 (x):''this is a function' 'time.sleep (1) print (x) func0 (' hello') print (func0.__name__) print (help (func0))

Running result:

Hello

Running time: 1.011878490447998

Wrapper

Help on function wrapper in module main:

Wrapper (* args, * * kwargs)

This is a decorator.

None

Whoo-hoo, it's out of the bag.

The solution is to assign the properties and methods of the original function to the wrapper in the decorator

Import timedef outter (a): def wrapper (* args, * * kwargs):''this is the decorator' 'start = time.time () a (* args) * * kwargs) end = time.time () print ('run time: {}' .format (end-start)) wrapper.__name__ = a.roomdocking _ return wrapper@outter # func0 = outter (func0) def func0 (x):''this is the function' 'time.sleep (1) print (x) func0 ( 'hello') print (func0.__name__) print (help (func0))

Running result:

Hello

Running time: 1.0030155181884766

Func0

Help on function func0 in module main:

Func0 (* args, * * kwargs)

This is a function.

None

However, functions have many properties and methods, one by one is too troublesome to modify manually, and may even be omitted, but python also provides a solution

Import timefrom functools import wrapsdef outter (a): @ wraps (a) def wrapper (* args, * * kwargs):''this is the decorator' 'start = time.time () a (* args) * * kwargs) end = time.time () print ('run time: {}' .format (end-start)) # wrapper.__name__ = a.run time: time.sleep (1) print (x) Func0 ('hello') print (func0.__name__) print (help (func0))

Running result:

Hello

Running time: 1.0114128589630127

Func0

Help on function func0 in module main:

Func0 (x)

This is a function.

None

4. Parameter decorator

Parameters are required in the decorator, but due to the limitation of syntax sugar, the decorator can only have one parameter, and this parameter is only used to receive the memory address of the decorated object. How to pass in other parameters?

Solution: turn the decorator into a closure function

Def outter (db_type): # decorator auth def auth (x): def wrapper (* args, * * kwargs): if db_type = = 'file': name = input (' Please enter name:') passwd = input ('Please enter password:') if name = 'zhangsan' and passwd = =' 123: X (* args) * * kwargs) print ('file-based authentication') else: print ('incorrect username or password Authentication failed') elif db_type = 'mysql': x (* args, * * kwargs) print (' authentication based on database') else: print ('unknown authentication method The') return wrapper return auth# function auth = outter (db_type='file') @ authdef file (): print ('hello') auth = outter (db_type='mysql') @ authdef mysql (): print (' world') msg = input ('Please choose the authentication method (1=file | 2=mysql):'). Strip () if msg = '1authentication: file () elif msg = =' 2customers: mysql () else: print ('not supported')

Write the passed parameters to the syntax sugar

Def outter (db_type): # decorator auth def auth (x): def wrapper (* args, * * kwargs): if db_type = = 'file': name = input (' Please enter name:') passwd = input ('Please enter password:') if name = 'zhangsan' and passwd = =' 123: X (* args) * * kwargs) print ('file-based authentication') else: print ('incorrect username or password Authentication failed') elif db_type = 'mysql': x (* args, * * kwargs) print (' authentication based on database') else: print ('unknown authentication method The') return wrapper return auth# function # auth = outter (db_type='file') # @ auth@outter (db_type='file') def file (): print ('hello') # auth = outter (db_type='mysql') # @ auth@outter (db_type='mysql') def mysql (): print (' world') msg = input ('Please select authentication method (1=file | 2=mysql):') .strip () if msg = '1percent: file () elif msg = =' 2percent: mysql () else: print ('not supported')

Template

# Parametric decorator template def out_decorator_name (XMagneyMagnez): def decorator_name (a): def wrapper (* args, * * kwargs): #. The newly added function. # below is the format of calling the original function a (* args, * * kwargs) return wrapper return decorator_name@out_decorator_name (XMagany Zeg1) def func_name (): pass above is all the content of this article entitled "knowledge points related to python decorators". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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