Question

如何检查某个对象是否已在python中初始化？我在多个地方有my_tac = tac(EDL_port)，如果它已经初始化，则会抛出如下所示的错误..我想添加一个检查，如果my_tac是是否初始化，如何做到这一点？代码： -

#From another file
my_tac = tac(EDL_port)

#alpha.py
class tac:
   ## tac class constructor.
   #
   #  @param self
   #  @param timeout
   #  @param baud_rate
   def __init__(self, port=None, timeout=0.3, baud_rate=115200):
      if port is not None:
         self.port = port
         self.ser = serial.Serial(self.port, baud_rate, timeout=timeout)
         return
      else:
         (tac_ports,spider_ports) = tac_probe_for_devices()
         print "TAC ports..."
   ......................

错误： -

11/5/2016 8:54:05 PM: my_tac = tac(EDL_port)
11/5/2016 8:54:05 PM: File "C:\CST_QSPR\third_party_bin\BuildLoaderScripts\Android\android_dl\alpaca.py", line 90, in __init__
11/5/2016 8:54:05 PM: self.ser = serial.Serial(self.port, baud_rate, timeout=timeout)
11/5/2016 8:54:05 PM: File "C:\Python27\lib\site-packages\serial\serialwin32.py", line 31, in __init__
11/5/2016 8:54:05 PM: ERROR:adb -s C2687475 remount failed
11/5/2016 8:54:05 PM: super(Serial, self).__init__(*args, **kwargs)
11/5/2016 8:54:05 PM: File "C:\Python27\lib\site-packages\serial\serialutil.py", line 236, in __init__
11/5/2016 8:54:05 PM: self.open()
11/5/2016 8:54:05 PM: File "C:\Python27\lib\site-packages\serial\serialwin32.py", line 62, in open
11/5/2016 8:54:05 PM: raise SerialException("could not open port {!r}: {!r}".format(self.portstr, ctypes.WinError()))
11/5/2016 8:54:05 PM: serial.serialutil.SerialException: could not open port 'COM8': WindowsError(5, 'Access is denied.')

Answer 1

您在这里看到的是Singleton设计模式。这种方法的关键思想是对象只能实例化一次。第二次尝试实例化它时，您将获得相同的对象。它可以像您的情况一样方便地访问数据库或创建端口句柄。没有真正的方法可以在python中使单例出类。但是，您可以将类转换为模块tac.py。 python中的模块默认是单例。对于初始化，您可以定义init(port=None, timeout=0.3, baud_rate=115200)函数，该函数将采用任何必需的参数。

# tac.py

port = None

def init(myport=None, timeout=0.3, baud_rate=115200):
    if myport is not None:
       global port
       port = myport
       ser = serial.Serial(port, baud_rate, timeout=timeout)
       return
    else:
       tac_ports, spider_ports = tac_probe_for_devices()
       print "TAC ports..."

def tac_probe_for_devices():
    # Probe some devices
    pass

import tac
tac.init(8080)

# From another file
import tac
print 'Tac port: ', tac.port  # Print 8080

请查看this帖子了解更多实施细节。

Answer 2

OP要求它，OP收到它。这是单例模式的一个例子，只分解为一个类。

class Test :
    count = 0
    def __init__(self, value) :
        if self.__class__.count > 0 :
            raise Exception
        else :
            self.__class__.count += 1
            self.value = value          #for the sake of the example


t1 = Test(12)      #instantiates the object
t2 = Test(27)      #throws an error

使用Python 3.4.3进行测试。

Answer 3

有多种方法可以解决这个问题。但是，我相信Singleton design pattern是解决这个问题最优雅的方法。

有关信息。关于如何实现Singleton设计模式，请参考以下

Creating a singleton in Python

Answer 4

这是设置单例类并将端口传递给它的方法。只需从SingletonClass继承你的tac类。这里有一个技巧，以确保您不会两次致电__init__。看看我如何检查super(self.__class__, self).__init__()的返回以确保它没有发生。

# tac.py

class SingletonClass(object):

    _inst = None
    _init_called = False

    def __new__(typ, *args, **kwargs):

        if SingletonClass._inst is None:
            obj = object.__new__(typ, *args, **kwargs)
            SingletonClass._inst = obj

        return SingletonClass._inst

    def __init__(self):

        # Call init inly on first instantiation if this class
        if SingletonClass._init_called:
            return True
        SingletonClass._init_called = True

class MyClass(SingletonClass):

    def __init__(self, port):

        if super(self.__class__, self).__init__():
            return

        self._port = port
        self._connections = '[D] Connection on port: %s' % self._port

    def connection(self):
        return self._connections

# From another file
from tac import MyClass

con = MyClass(8080)
print 'First connection id: ', id(con)
print con.connection()

con = MyClass(5000)
print 'Second connection id: ', id(con)
print con.connection()

如何检查对象是否已在python中初始化？

4 个答案: