一、单例模式简介
概述：要求一个类有且仅有一个实例，并且提供了一个全局的访问点。
应用场景：日志插入、计时器、权限校验、回收站、网站计数器、线程池、数据库连接池等资源池。
二、日志记录器的实现
一个对象的实例化过程是先执行类的__new__方法,如果我们没有写,默认会调用object的__new__方法,返回一个实例化对象,然后再调用__init__方法,对这个对象进行初始化,我们可以根据这个实现单例.
在一个类的__new__方法中先判断是不是存在实例,如果存在实例,就直接返回,如果不存在实例就创建.
# coding=utf-8
class Singleton(object):
"""
单例类
"""
_instance = None
def __new__(cls, *args, **kwargs):
if not cls._instance:
cls._instance = super(Singleton, cls).__new__(cls) # python3
# cls._instance = super(Singleton, cls).__new__(cls，*args, **kwargs) # python2
return cls._instance
class Logger(Singleton):
"""
日志
"""
def __init__(self, file_name):
self.filename = file_name
def _write_log(self, level, msg):
with open(self.filename, "a") as log_file:
log_file.write("[{0}]{1}\n".format(level, msg))
def critical(self, msg):
self._write_log("CRITICAL", msg)
def error(self, msg):
self._write_log("ERROR", msg)
def warn(self, msg):
self._write_log("WARN", msg)
def info(self, msg):
self._write_log("INFO", msg)
def debug(self, msg):
self._write_log("DEBUG", msg)
if __name__ == '__main__':
log1 = Logger("logger1.log")
log2 = Logger("logger2.log")
print(id(log1), log1.filename)
print(id(log2), log2.filename)
log1.info("log1************")
log1.warn("log1************")
log2.info("log2************")
log2.warn("log2************")
控制台输出如下：
566521222648 logger2.log
566521222648 logger2.log
生成一个logger2.log文件，文件内容如下：
[INFO]log1************ [WARN]log1************ [INFO]log2************ [WARN]log2************
结果表明：日志信息内容记录在同一个文件中
参考资料
[Wessel Badenhorst]Practical Python Design Patterns：Pyrhonic Solution to Common Problems
https://blog.csdn.net/sxb0841901116/article/details/78506643
https://www.runoob.com/design-pattern/singleton-pattern.html