Scenarios Python decorators

Scenarios decorator

Additional features
Data cleanup or add:
- Parameter type validation function similar to the previous request interceptor @require_ints
- After the data format conversion function returns the dictionary to JSON / YAML similar response tamper
- Provide additional data as a function of mock.patch
Registration function
- Register a task in the task center
- A registration function with the signal processor

Decorators to achieve under different scenarios

Functions Registry

Simple Registry

funcs = []
def register(func):
    funcs.append(func)
    return func
    
    
@register
def a():
    return 3
    
@register
def b():
    return 5
    

# 访问结果
result = [func() for func in funcs]

Registry isolation (using different instances of the class)


class Registry(object):
    def __init__(self):
        self._funcs = []
    
    def register(self, func):
        self._funcs.append(func)
        
    def run_all(self):
        return [func() for func in self._funcs]
        
        
r1 = Registry()
r2 = Registry()

@r1.register
def a():
    return 3
    
@r2.register
def b():
    return 5
    
@r1.register
@r2.register

Code is executed when the package

Type checking

from functools import wraps

def require_ints(func):
    @wraps(func)  # 将func的信息复制给inner
    def inner(*args, **kwargs):
        for arg list(args) + list(kwargs.values()):
            if not isinstance(arg, int:
                raise TypeError("{} 只接受int类型参数".format(func.__name__)
        return func(*args, **kwargs)
    return inner

User Authentication

from functools import wraps

class User(object):
    def __init__(self, username, email):
        self.username = username
        self.email = email
        
class AnonymousUser(object):
    def __init__(self):
        self.username = self.email = None
        
    def __nonzero__(self):  # 将对象转换为bool类型时调用
        return False
        
def requires_user(func):
    @wraps(func)
    def inner(user, *args, **kwargs):  # 由于第一个参数无法支持self, 该装饰器不支持装饰类
        if user and isinstance(user, User):
            return func(use, *args, **kwargs)
        else:
            raise ValueError("非合法用户")
    return inner

Output Format

import json
from functools import wraps

def json_output(func):  # 将原本func返回的字典格式转为返回json字符串格式
    @wrap(func)
    def inner(*args, **kwargs):
        return json.dumps(func(*args, **kwargs))
    return inner

Exception trap

import json
from functools import wraps

class Error1(Exception):
    def __init__(self, msg):
        self.msg = msg
    def __str__(self):
        return self.msg
        

def json_output(func):
    @wrap(func)
    def inner(*args, **kwargs):
        try:
            result = func(*args, **kwargs)
        except Error1 as ex:
            result = {"status": "error", "msg": str(ex)}
        return json.dumps(result)
    return inner

# 使用方法
@json_ouput
def error():
    raise Error1("该条异常会被捕获并按JSON格式输出")

Log Management

import time
import logging
from functools import wraps

def logged(func):
    @wraps(func)
    def inner(*args, **kwargs):  # *args可以装饰函数也可以装饰类
        start = time.time()
        result = func(*args, **kwargs)
        exec_time = time.time() - start
        logger = logging.getLoger("func.logged")
        logger.warning("{} 调用时间:{:.2} 执行时间:{:.2}s 结果:{}".format(func.__name__, start, exec_time, result)

Decorator with parameters

Decorator with parameters corresponding to a decorator return function, @deco(a=1)the call @before the first execution will deco(a=1)get a real decorator, decorator with parameters deco(a=1)executed immediately when the module is introduced

Decoration

(When not expanded by subclasses super method, such as a plurality of classes need to add this functionality) increase the sorting class

import time
from functools import wraps

def sortable_by_created(cls):
    original_init = cls.__init__
    
    @wrap(original_init)
    def new_init(self, *args, **kwargs):
        original_init(*args, **kwargs)
        self._created = time.time()
    
    cls.__init__ = new_init
    
    cls.__lt__ = lambda self, other: self._created < other._created
    cls.__gt__ = lambda self, other: self._created > other._created
    return cls

Also define a SortableByCreated () class, subclass and its superclass using multiple inheritance SortableByCreated

Type Conversion

There may be decorated after the function becomes an instance of a class, this time for compatibility function calls should be provided for the class returned by __call__the method

class Task(object):
    def __call__(self, *args, **kwargs):
        return self.run(*args, **kwargs)
    def run(self, *args, **kwargs):
        raise NotImplementedError("子类未实现该接口")
        
def task(func):
    class SubTask(Task):
        def run(self, *args, **kwargs):
            func(*args, **kwargs)
    return SubTask()

Chapter II context manager

definition

Packaging arbitrary code
Ensure consistency of execution

grammar

with statement
__enter__ method and __exit__

class ContextManager(object):
    def __init__(self):
        self.entered = False
        
    def __enter__(self):
        self.entered = True
        return self
        
    def __exit__(self, exc_type, exc_instance, traceback):
        self.entered = False

Scenarios

Resource Cleanup

import pymysql

class DBConnection(object):
    def __init__(self, *args, **kwargs):
        self.args,self.kwargs = args, kwargs
        
    def __enter__(self):
        self.conn = pymysql.connect(*args, **kwargs)
        return self.conn.cursor()
        
    def __exit__(self, exc_type, exc_instance, trackback):
        self.conn.close()

Exception handling (to avoid repetition)

Abnormal propagation (in the __exit__ return False)
Abnormal termination (__exit__ in return True)

class BubleExceptions(object):
    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_instance, trackback):
        if exc_instance:
            print("出现异常: {}".format(exc_instance)
        return False   # return True终止异常

Deal with specific exceptions

class HandleValueError(object):
    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_instance, trackback):
        if not exc_type: return True
        if issubclass(exc_type, ValueError): 
            print("处理ValueError: {}".format(exc_instance)
        return False

if issubclass...Statement to if exec_type == ValueErrorValueType not process a subclass

It may also be determined whether or terminated in accordance with the propagation property abnormality

Simpler syntax

import contextlib

@contextlib.contextmanager
def acceptable_error_codes(*codes):
    try:
        yield
    except ShellException as exc_instance:
        if exc_instance.code not in codes:
            raise
        pass