Python进阶强化训练之装饰器使用技巧进阶

转载博客地址：https://ansheng.me/

内容源自刘硕老师的《Python进阶强化训练》

视频课程：http://coding.imooc.com/class/62.html

如何使用函数装饰器？

解决方案

# 函数装饰器
def memp(func):
cache = {}
def wrap(*args):
if args not in cache:
cache[args] = func(*args)
return cache[args]
return wrap
# 第一题
@memp
def fibonacci(n):
if n <= 1:
return 1
return fibonacci(n - 1) + fibonacci(n - 2)
print(fibonacci(50))
# 第二题
@memp
def climb(n, steps):
count = 0
if n == 0:
count = 1
elif n > 0:
for step in steps:
count += climb(n - step, steps)
return count
print(climb(10, (1, 2, 3)))

C:\Python\Python35\python.exe E:/python-intensive-training/s11.py
20365011074
274
Process finished with exit code 0

如何为被装饰的函数保存元数据？

f.__name__

f.__doc__

f.__module__

f.__dict__

f.__defaults__

解决方案

functools

wraps

from functools import wraps
def mydecoratot(func):
@wraps(func)
def wrapper(*args, **kwargs):
"""wrapper function"""
print("In wrapper")
func(*args, **kwargs)
return wrapper
@mydecoratot
def example():
"""example function"""
print('In example')
print(example.__name__)
print(example.__doc__)

如何定义带参数的装饰器？

解决方案

typeassert

from inspect import signature
def typeassery(*ty_args, **ty_kwargs):
def decorator(func):
# 获取到函数参数和类型之前的关系
sig = signature(func)
btypes = sig.bind_partial(*ty_args, **ty_kwargs).arguments
def wrapper(*args, **kwargs):
for name, obj in sig.bind(*args, **kwargs).arguments.items():
if name in btypes:
if not isinstance(obj, btypes[name]):
raise TypeError('"%s" must be "%s" ' % (name, btypes[name]))
return func(*args, **kwargs)
return wrapper
return decorator
@typeassery(int, str, list)
def f(a, b, c):
print(a, b, c)
# 正确的
f(1, 'abc', [1, 2, 3])
# 错误的
f(1, 2, [1, 2, 3])

如何实现属性可修改的函数装饰器？

解决方案

from functools import wraps
import time
import logging
from random import randint
def warn(timeout):
# timeout = [timeout]  # py2
def decorator(func):
def wrapper(*args, **kwargs):
start = time.time()
res = func(*args, **kwargs)
used = time.time() - start
if used > timeout:
# if used > timeout:  # py2
msg = '"%s": "%s" > "%s"' % (func.__name__, used, timeout)
# msg = '"%s": "%s" > "%s"' % (func.__name__, used, timeout[0])  # py2
logging.warn(msg)
return res
def setTimeout(k):
nonlocal timeout
timeout = k
# timeout[0] = k  # py2
wrapper.setTimeout = setTimeout
return wrapper
return decorator
@warn(1.5)
def test():
print('In Tst')
while randint(0, 1):
time.sleep(0.5)
for _ in range(10):
test()
test.setTimeout(1)
for _ in range(10):
test()

如何在类中定义装饰器？

解决方案

import logging
from time import localtime, time, strftime, sleep
from random import choice
class CallingInfo:
def __init__(self, name):
log = logging.getLogger(name)
log.setLevel(logging.INFO)
fh = logging.FileHandler(name + '.log')  # 日志保存的文件
log.addHandler(fh)
log.info('Start'.center(50, '-'))
self.log = log
self.formattter = '%(func)s -> [%(time)s - %(used)s - %(ncalls)s]'
def info(self, func):
def wrapper(*args, **kwargs):
wrapper.ncalls += 1
lt = localtime()
start = time()
res = func(*args, **kwargs)
used = time() - start
info = {}
info['func'] = func.__name__
info['time'] = strftime('%x %x', lt)
info['used'] = used
info['ncalls'] = wrapper.ncalls
msg = self.formattter % info
self.log.info(msg)
return res
wrapper.ncalls = 0
return wrapper
def SetFormatter(self, formatter):
self.formattter = formatter
def turnOm(self):
self.log.setLevel(logging.INFO)
def turnOff(self):
self.log.setLevel(logging.WARN)
cinfo1 = CallingInfo('mylog1')
cinfo2 = CallingInfo('mylog2')
# 设置日志指定格式
# cinfo1.SetFormatter('%(func)s -> [%(time)s - %(ncalls)s]')
# 关闭日志
# cinfo2.turnOff()
@cinfo1.info
def f():
print('in F')
@cinfo1.info
def g():
print('in G')
@cinfo2.info
def h():
print('in H')
for _ in range(50):
choice([f, g, h])()
sleep(choice([0.5, 1, 1.5]))

转载博客地址：https://ansheng.me/

内容源自刘硕老师的《Python进阶强化训练》

视频课程：http://coding.imooc.com/class/62.html