我有一个使用 Python/NXT/libusb 的简单工作示例，如下所示(注意:使用具有 USB 接口(interface)的乐高 NXT):
import nxt.locator
from nxt.motor import *
def flip_cube(b):
m_arm = Motor(b, PORT_B)
m_arm.turn(75, 85)
m_arm.turn(-50, 85)
b = nxt.locator.find_one_brick()
flip_cube(b)
以上工作正常。
作为训练练习，我尝试“对象化”python 代码，这样我就可以开始在代码周围放置库，但现在 LibUSB 库提示它找不到 USB 设备。嗯？我究竟做错了什么。这是我尝试使用类结构的代码:
import nxt.locator
from nxt.motor import *
class BasicRobotTestCase():
__test__ = True
def __init__(self):
b = nxt.locator.find_one_brick()
def flip_cube(self):
m_arm = Motor(b, PORT_B)
m_arm.turn(75, 85)
m_arm.turn(-50, 85)
def test_flip_cube(self):
flip_cube()
当我执行上面的代码时，出现以下错误(即使我重新执行第一个示例，它再次执行正常):
E
======================================================================
ERROR: Failure: USBError (No such device (it may have been disconnected))
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Library/Python/2.6/site-packages/nose-0.11.4-py2.6.egg/nose/loader.py", line 485, in makeTest
return self._makeTest(obj, parent)
File "/Library/Python/2.6/site-packages/nose-0.11.4-py2.6.egg/nose/loader.py", line 539, in _makeTest
return MethodTestCase(obj)
File "/Library/Python/2.6/site-packages/nose-0.11.4-py2.6.egg/nose/case.py", line 331, in __init__
self.inst = self.cls()
File "/Users/gnunez/git-projects/pdca_automation/rubics/tests/basic_robot_test_case.py", line 8, in __init__
b = nxt.locator.find_one_brick()
File "/Users/gnunez/git-projects/pdca_automation/nxt/locator.py", line 112, in find_one_brick
for s in find_bricks(host, name, silent, method):
File "/Users/gnunez/git-projects/pdca_automation/nxt/locator.py", line 43, in find_bricks
for s in socks:
File "/Users/gnunez/git-projects/pdca_automation/nxt/usbsock.py", line 83, in find_bricks
for bus in usb.busses():
File "build/bdist.macosx-10.6-universal/egg/usb/legacy.py", line 330, in busses
return (Bus(),)
File "build/bdist.macosx-10.6-universal/egg/usb/legacy.py", line 326, in __init__
self.devices = [Device(d) for d in core.find(find_all=True)]
File "build/bdist.macosx-10.6-universal/egg/usb/legacy.py", line 311, in __init__
self.configurations = [Configuration(c) for c in dev]
File "build/bdist.macosx-10.6-universal/egg/usb/core.py", line 706, in __iter__
yield Configuration(self, i)
File "build/bdist.macosx-10.6-universal/egg/usb/core.py", line 407, in __init__
configuration
File "build/bdist.macosx-10.6-universal/egg/usb/_debug.py", line 52, in do_trace
return f(*args, **named_args)
File "build/bdist.macosx-10.6-universal/egg/usb/backend/libusb10.py", line 423, in get_configuration_descriptor
config, byref(cfg)))
File "build/bdist.macosx-10.6-universal/egg/usb/backend/libusb10.py", line 357, in _check
raise USBError(_str_error[retval.value])
USBError: No such device (it may have been disconnected)
请您参考如下方法:
创建 BasicRobotTestCase 时，如果不将 b 变量存储为实例的成员(即 self.b)，则会丢失 b 变量
编辑: 好吧，丢失的 self 不是问题的根源，也许 nose 实例化你的类的方式改变了一些东西到 USB 抓取，尝试实例化直接上课。
import nxt.locator
from nxt.motor import *
class BasicRobotTestCase():
__test__ = True
def __init__(self):
self.b = nxt.locator.find_one_brick() # Store the brick in self.b
def flip_cube(self):
m_arm = Motor(self.b, PORT_B) # use the stored brick in self.b to create the motor
m_arm.turn(75, 85)
m_arm.turn(-50, 85)
def test_flip_cube(self):
self.flip_cube()
if __name__=="__main__":
BasicRobotTestCase().test_flip_cube()
