Python 2.7 - Classes

Question

我正在尝试在python (perfmon)中编辑库-该文件是session.py

我想添加一个模块，可以从USB端口记录一些读数。

这也是我第一次试用python中的类。

from perfmon import *
import os
import sys
import serial

# Common base class
class Session:
  def __init__(self, events):
    self.system = System()
    self.event_names = events
    self.events = []
    self.fds = []
    for e in events:
      err, encoding = pfm_get_perf_event_encoding(e, PFM_PLM0 | PFM_PLM3,
                                                  None, None)
      self.events.append(encoding)
    self.USB = serial.Serial("/dev/ttyUSB0",115200)

  def __del__(self):
    pass

  def read(self, fd):
    # TODO: determine counter width
    return os.read(fd, 8)

class PerThreadSession(Session):
  def __init__(self, pid, events):
    self.pid = pid
    Session.__init__(self, events)

  def __del__(self):
    Session.__del__(self)

  def start(self):
    for e in self.events:
      self.fds.append(perf_event_open(e, self.pid, -1, -1, 0))

  def read(self, i):
    return Session.read(self, self.fds[i])

class USB(Session):
  def __init__(self):   
    return self.USB

这是我得到的以下错误：

Python 2.7.3 (default, Apr 14 2012, 08:58:41) [GCC] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import perfmon
>>> test = perfmon.USB()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'USB'

我正在做的错误是什么？我知道self在python中是一个构造器，我可以在那里返回值吗？

Answer 1

据我所知，你的答案是

>>> from perfmon import session
>>> test = session.USB()

但是你这样做是错误的。您应该在您的工作区/项目目录中创建自己的模块。导入会话模块并在其中创建类

from perfmon import session
class USB(Session):
    def __init__(self):   
        pass #I have changed this part as It has two errors in your example

Answer 2

您不能从类构造函数返回任何内容(除了None之外)。

否则将会有一个

TypeError: __init__() should return None