Python Windows 上的 Pyusb - 没有可用的后端
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Pyusb on windows - no backend available
提问by user634340
I'm trying to have my python application interface with an NFC device via USB. The best option seems to be pyusb, but I can't get it to connect to the libusb backend. I keep getting
我正在尝试通过 USB 将我的 python 应用程序接口与 NFC 设备连接起来。最好的选择似乎是 pyusb，但我无法让它连接到 libusb 后端。我不断得到
ValueError: No backend available
ValueError：没有可用的后端
I've looked at the stack trace, and found that usb/backend/libusb10.py(which is part of pyusb) is trying to load libusb-1.0.dllto use as the backend, but it can't find it. It's not that its not in my path, its not on my computer at all!
我查看了堆栈跟踪，发现usb/backend/libusb10.py（它是 pyusb 的一部分）正在尝试加载libusb-1.0.dll以用作后端，但找不到它。并不是它不在我的路径中，它根本不在我的电脑上！
I have installed libusb-win32 (http://libusb.org/wiki/libusb-win32), but the resulting directory only seems to include libusb0.dll. Where is libusb-1.0.dll???!
我已经安装了 libusb-win32 ( http://libusb.org/wiki/libusb-win32)，但结果目录似乎只包含 libusb0.dll。libusb-1.0.dll 在哪里？？？
I would love to know either where to get that dll, or even a different suggestion to get pyusb to work on Windows 7.
我很想知道从哪里获得那个 dll，或者甚至是让 pyusb 在 Windows 7 上工作的不同建议。
回答by Dave L.
I had a similar issue recently trying to talk to a USB device I am developing. I scoured the web looking for libusb-1.0.dll's and had no luck. I found source code, but nothing built and ready to install. I ended up installing the libusb-win32 binaries, which is the libusb0.dll.
我最近在尝试与我正在开发的 USB 设备交谈时遇到了类似的问题。我在网上搜索 libusb-1.0.dll 并没有走运。我找到了源代码，但没有构建和准备安装。我最终安装了 libusb-win32 二进制文件，即 libusb0.dll。
PyUSB will search for libusb-1.0, libusb0, and openUSB backends.
PyUSB 将搜索 libusb-1.0、libusb0 和 openUSB 后端。
libusb0.dll was already on my system, but something was still not set up right, do PyUSB was not working.
libusb0.dll 已经在我的系统上，但仍然没有正确设置，PyUSB 是否不起作用。
I followed the directions hereto download and install the driver using the GUI tools provided to install the filter driver, and the INF wizard. Note, it didn't work until I ran the INF wizard.
我按照此处的说明使用提供的 GUI 工具下载和安装驱动程序，以安装过滤器驱动程序和 INF 向导。请注意，直到我运行 INF 向导它才起作用。
I'm pretty new to programming and I've found the lack of clear documentation/examples to string this all together rather frustrating.
我对编程还很陌生，我发现缺乏清晰的文档/示例来将这一切串联在一起，这令人沮丧。
回答by George G
I am using Python 2.6.5, libusb-win32-device.bin-0.1.12.1and pyusb-1.0.0-a0on a windows XP system and kept receiving ValueError: No backend available.
我正在使用 Python 2.6.5，libusb-win32-device.bin-0.1.12.1并pyusb-1.0.0-a0在 Windows XP 系统上不断接收ValueError: No backend available.
Since there wasn't any real help on the web for this problem I spent a lot of time finding that ctypes util.pyuses the Pathvariable to find the library file. My pathdid not include windows\system32and PYUSBdidn't find the library. I updated the pathvariable and now the USB is working.
由于网络上没有针对此问题的任何真正帮助，因此我花了很多时间寻找ctypes util.py使用该Path变量来查找库文件的方法。我path不包括windows\system32和PYUSB没找到库。我更新了path变量，现在 USB 正在工作。
回答by tbenisa
To connect to your NFC device via USB using PYUSB, you will need to install the backend for that device. I do not think there is any backend for any device other than a libusb device.
要使用 PYUSB 通过 USB 连接到您的 NFC 设备，您需要为该设备安装后端。我认为除了 libusb 设备之外，任何设备都没有任何后端。
To build a backend. You will need to know the driver (.sys file) for your device, so you could write a wrapper DLL to expose functionalities in the device. Your DLL would have to have a method to find device based on PID & VID, another method to open device and another method to send data and so on...
建立一个后端。您将需要知道您的设备的驱动程序（.sys 文件），以便您可以编写一个包装 DLL 来公开设备中的功能。您的 DLL 必须有一种基于 PID 和 VID 查找设备的方法、另一种打开设备的方法和另一种发送数据的方法等等......
回答by Liviu
"There are two versions of the libusb API: the current libusb-1.0API, and its legacy predecessor libusb-0.1." (http://www.libusb.org/) "libusb-win32is a port of the USB library ?libusb-0.1to the Microsoft Windows operating systems". "Download the latest release tarball" from the same page(1.0.9is the current version) to have libusb-1.0equivalent, you'll find a folder Win32, where you'll find your libusb-1.0.dllto play with! You can even build it: http://www.libusb.org/wiki/windows_backend.
“libusb API 有两个版本：当前的libusb-1.0API 和它的旧版 API libusb-0.1。” ( http://www.libusb.org/) “libusb-win32是 USB 库的端口？libusb-0.1到 Microsoft Windows 操作系统”。从同一页面（1.0.9是当前版本）“下载最新版本的 tarball”以获取libusb-1.0等效文件，您会找到一个文件夹Win32，您可以在其中找到libusb-1.0.dll要玩的！您甚至可以构建它：http: //www.libusb.org/wiki/windows_backend。
EDITYou have to build it (download from/ http://sourceforge.net/projects/libusb/files/libusb-1.0/) since the tarball is from 2012, while the latest sources are from 2014-06-15.
编辑您必须构建它（从/ http://sourceforge.net/projects/libusb/files/libusb-1.0/下载），因为 tarball 来自 2012，而最新的来源来自 2014-06-15。
回答by fixxxer
Just in case:
以防万一：
I haven't tried this on Windows but I had to set DYLD_LIBRARY_PATH path to circumvent this error on the Macintosh.
我没有在 Windows 上尝试过这个，但我必须设置 DYLD_LIBRARY_PATH 路径来规避 Macintosh 上的这个错误。
export DYLD_LIBRARY_PATH=/opt/local/lib
导出 DYLD_LIBRARY_PATH=/opt/local/lib
Discussion on whether or not to set this variable is here.
关于是否设置这个变量的讨论在这里。
回答by beebek
Download and install libusb-win32-devel-filter-1.2.6.0.exe. It should work.
下载并安装libusb-win32-devel-filter-1.2.6.0.exe。它应该工作。
回答by user9393931
I had the same problem with Windows 10, both Python 2.7.16 and Python 3.7.2. I installed libusb (through python -m pip install libusb) but the error message remained. Also, the advice above about installing libusb-win32 did not work for me; neither of the 2 links (original post and @beebek's answer) existed.
我在 Windows 10 上遇到了同样的问题，包括 Python 2.7.16 和 Python 3.7.2。我安装了 libusb（通过python -m pip install libusb），但错误消息仍然存在。另外，上面关于安装 libusb-win32 的建议对我不起作用；两个链接（原始帖子和@beebek 的答案）都不存在。
What didwork, however, is the comment by @user1495323 : I copied libusb-1.0.dllfrom
C:\Users\username\AppData\Roaming\Python\Python27\site-packages\libusb\_platform\_windows\x64\to C:\Windows\System32\
什么做工作，但是，是@ user1495323评论：我复制libusb-1.0.dll从
C:\Users\username\AppData\Roaming\Python\Python27\site-packages\libusb\_platform\_windows\x64\到C:\Windows\System32\
回答by Sergey Lourie
There's a simpler solution.
有一个更简单的解决方案。
Download and unpack to C:\PATH the libusb-1.0.20 from download link
从下载链接下载libusb-1.0.20 并解压到 C:\PATH
Then try this line:
然后试试这一行：
backend = usb.backend.libusb1.get_backend(find_library=lambda x: "C:\PATH\libusb-1.0.20\MS32\dll\libusb-1.0.dll")
dev = usb.core.find(backend=backend, find_all=True)
backend = usb.backend.libusb1.get_backend(find_library=lambda x: "C:\PATH\libusb-1.0.20\MS32\dll\libusb-1.0.dll")
dev = usb.core.find(后端=后端，find_all=True)
Depending on your system, try either MS64 or MS32 version of the .dll
根据您的系统，尝试使用 MS64 或 MS32 版本的 .dll
Update of 17/01/2020, after a request to share more code:
2020 年 1 月 17 日更新，请求共享更多代码后：
import usb.core
import usb.util
from infi.devicemanager import DeviceManager
dm = DeviceManager()
devices = dm.all_devices
for i in devices:
try:
print ('{} : address: {}, bus: {}, location: {}'.format(i.friendly_name, i.address, i.bus_number, i.location))
except Exception:
pass
import usb.backend.libusb1
backend = usb.backend.libusb1.get_backend(find_library=lambda x: "C:\libusb-1.0.20\MS32\dll\libusb-1.0.dll")
dev = usb.core.find(backend=backend, find_all=True)
def EnumerateUSB(): #I use a simple function that scans all known USB connections and saves their info in the file
with open("EnumerateUSBLog.txt", "w") as wf:
counter = 0
for d in dev:
try:
wf.write("USB Device number " + str(counter) + ":" + "\n")
wf.write(d._get_full_descriptor_str() + "\n")
wf.write(d.get_active_configuration() + "\n")
wf.write("\n")
counter += 1
except NotImplementedError:
wf.write("Device number " + str(counter) + "is busy." + "\n")
wf.write("\n")
counter += 1
except usb.core.USBError:
wf.write("Device number " + str(counter) + " is either disconnected or not found." + "\n")
wf.write("\n")
counter += 1
wf.close()
