Python装饰器

1. 简单装饰器

import time

def timer(func):
    def wrapper(*args,**kwargs):
        t1 = time.time()
        func(*args,**kwargs)
        t2 = time.time()
        run_time = t2 - t1
        print(run_time)
    return wrapper

@timer
def foo():
    time.sleep(3)
#
foo()                   # 3.0006301403045654
foo = timer(foo)        # 等同于使用timer装饰器
foo()                   # 3.0006301403045654

2. 带参数的装饰器

import logging

def log(level):
    def decorator(func):
        def wrapper(*args,**kwargs):
            if level == 'warn':
                logging.warn("%s is running" % func.__name__)
            return func(*args,**kwargs)
        return wrapper
    return decorator

@log('warn')
def foo(a='123'):
    print('the number is %s' %a)

foo()
the number is 123
WARNING:root:foo is running

3. 类装饰器

import logging

def log(level):
    def decorator(func):
        def wrapper(*args,**kwargs):
            if level == 'warn':
                logging.warn("%s is running" % func.__name__)
            return func(*args,**kwargs)
        return wrapper
    return decorator

@log('warn')
def foo(a='123'):
    print('the number is %s' %a)

foo()
the number is 123
WARNING:root:foo is running

4. 类装饰器

import logging

def log(level):
    def decorator(func):
        def wrapper(*args,**kwargs):
            if level == 'warn':
                logging.warn("%s is running" % func.__name__)
            return func(*args,**kwargs)
        return wrapper
    return decorator

@log('warn')
def foo(a='123'):
    print('the number is %s' %a)

foo()
the number is 123
WARNING:root:foo is running

5. functools.wraps

#装饰器有个缺点，会改变原函数的元信息
#functools.wraps本身也是装饰器，可把元信息拷贝到装饰器函数中，使元信息和原装饰器一致
from functools import wraps
def logged(func):
    @wraps(func)
    def with_logging(*args,**kwargs):
        print(func.__name__ + "was called")
        return func(*args,**kwargs)
    return with_logging
@logged
def f(x):
    """does soma math"""
return x + x * x

print(f.__name__)
print(f.__doc__)

6. 装饰器顺序

@a
@b
@c
def f():
    pass
# 等价于
f = a(b(c(f)))