在安装otree时使用的"pip install -U channels"命令出现错误（执行setup.py bdist_wheel for twisted时出错...）。

为了使用 otree（http://otree.readthedocs.io/）项目，我尝试安装 Channels 以利用实时功能时遇到了一些问题。

由于输出很长，我试图找出最重要的部分：

查看完整输出，请参见：https://jsfiddle.net/L4ccmr2k/1/

我认为相关的输出已用红色标出。

1.

 Building wheels for collected packages: twisted
      Running setup.py bdist_wheel for twisted ... error

2.

creating build/temp.macosx-10.6-intel-3.6
      creating build/temp.macosx-10.6-intel-3.6/src
      creating build/temp.macosx-10.6-intel-3.6/src/twisted
      creating build/temp.macosx-10.6-intel-3.6/src/twisted/test
      /usr/bin/clang -fno-strict-aliasing -Wsign-compare -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -arch i386 -arch x86_64 -g -I/Library/Frameworks/Python.framework/Versions/3.6/include/python3.6m -c src/twisted/test/raiser.c -o build/temp.macosx-10.6-intel-3.6/src/twisted/test/raiser.o
      xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
      error: command '/usr/bin/clang' failed with exit status 1
      ----------------------------------------
      Failed building wheel for twisted
      Running setup.py clean for twisted
    Failed to build twisted
    Installing collected packages: twisted, daphne, channels
      Running setup.py install for twisted ... error
        Complete output from command /Library/Frameworks/Python.framework/Versions/3.6/bin/python3.6 -u -c "import setuptools, tokenize;__file__='/private/var/folders/6_/30pgp_bj17j3krgq_kt0py440000gn/T/pip-build-v4kcayoj/twisted/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /var/folders/6_/30pgp_bj17j3krgq_kt0py440000gn/T/pip-vpnlc5lo-record/install-record.txt --single-version-externally-managed --compile:

3.

creating build/temp.macosx-10.6-intel-3.6
    creating build/temp.macosx-10.6-intel-3.6/src
    creating build/temp.macosx-10.6-intel-3.6/src/twisted
    creating build/temp.macosx-10.6-intel-3.6/src/twisted/test
    /usr/bin/clang -fno-strict-aliasing -Wsign-compare -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -arch i386 -arch x86_64 -g -I/Library/Frameworks/Python.framework/Versions/3.6/include/python3.6m -c src/twisted/test/raiser.c -o build/temp.macosx-10.6-intel-3.6/src/twisted/test/raiser.o
    xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
    error: command '/usr/bin/clang' failed with exit status 1
    ----------------------------------------
Command "/Library/Frameworks/Python.framework/Versions/3.6/bin/python3.6 -u -c "import setuptools, tokenize;__file__='/private/var/folders/6_/30pgp_bj17j3krgq_kt0py440000gn/T/pip-build-v4kcayoj/twisted/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /var/folders/6_/30pgp_bj17j3krgq_kt0py440000gn/T/pip-vpnlc5lo-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /private/var/folders/6_/30pgp_bj17j3krgq_kt0py440000gn/T/pip-build-v4kcayoj/twisted/

我正在使用：

• macOS 10.12.6
• Python 2.7.10
• wheel-0.30.0
• pip 9.0.1 from /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (python 3.6)
• Django-1.8.8
• Twisted-16.2.0
• asgiref-0.14.0
• autobahn-0.16.0
• channels-0.17.3
• otree-core-1.4.28
• pytz-2016.6.1
• six-1.10.0
• txaio-2.5.1
• wheel-0.29.0
• zope.interface-4.2.0