参考：

在执行./run_demo.sh的过程中，遇到了python的模块问题：

root@ubuntu:/home/wasdns/tutorials/SIGCOMM_2015/source_routing# ./run_demo.sh ./run_demo.sh: line 31: /home/wasdns/tutorials/SIGCOMM_2015/source_routing/home/wasdns/p4c-bmv2/p4c_bm/__main__.py: No such file or directoryTraceback (most recent call last):  File "topo.py", line 23, in 
    
         from p4_mininet import P4Switch, P4HostImportError: No module named p4_mininet

p4_mininet.py所在的文件夹：/home/wasdns/bmv2/mininet

root@ubuntu:/home/wasdns# cd bmv2/root@ubuntu:/home/wasdns/bmv2# lsaclocal.m4      config.status  include          Makefile.in  test-driverautogen.sh      config.sub     install_deps.sh  mininet      testsautom4te.cache  configure      install-sh       missing      third_partycompile         configure.ac   libtool          pdfixed      thrift_srcconfig.guess    CPPLINT.cfg    LICENSE          py-compile   toolsconfig.h        depcomp        ltmain.sh        README.md    travisconfig.h.in     docs           m4               src          VERSIONconfig.h.in~    Doxyfile       Makefile         stamp-h1config.log      Doxymain.md    Makefile.am      targetsroot@ubuntu:/home/wasdns/bmv2# cd mininet/root@ubuntu:/home/wasdns/bmv2/mininet# ls1sw_demo.py         simple_router.p4          stress_test_ipv4.py.inp4_mininet.py       stress_test_commands.txtsimple_router.json  stress_test_ipv4.py

于是要把这个路径加入python的系统路径中，过程如下：

1.先找到python的系统路径：

root@ubuntu:/home/wasdns# pythonPython 2.7.6 (default, Oct 26 2016, 20:30:19) [GCC 4.8.4] on linux2Type "help", "copyright", "credits" or "license" for more information.>>> import sys>>> sys.path['', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-x86_64-linux-gnu', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/local/lib/python2.7/dist-packages/mininet-2.3.0d1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/setuptools-32.1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/pip-9.0.1-py2.7.egg', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PILcompat', '/usr/lib/python2.7/dist-packages/gtk-2.0', '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']>>> exit()

找到/usr/local/lib/python2.7/dist-packages这个路径。

cd /usr/local/lib/python2.7/dist-packages

2.增添.pth文件

root@ubuntu:/home/wasdns# cd /usr/local/lib/python2.7/dist-packagesroot@ubuntu:/usr/local/lib/python2.7/dist-packages# touch p4_mininet.pthroot@ubuntu:/usr/local/lib/python2.7/dist-packages# vim p4_mininet.pth/home/wasdns/bmv2/mininet

原因：

Python 在遍历已有的库文件目录（sys.path中指定）过程中，如果见到一个 .pth 文件，就会将该文件中所记录的路径加入到 sys.path 设置中，这样 .pth 文件说指明的库也就可以被 Python 运行环境找到。

3.查看路径，验证是否加入：

root@ubuntu:/usr/local/lib/python2.7/dist-packages# pythonPython 2.7.6 (default, Oct 26 2016, 20:30:19) [GCC 4.8.4] on linux2Type "help", "copyright", "credits" or "license" for more information.>>> import sys>>> sys.path['', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-x86_64-linux-gnu', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/local/lib/python2.7/dist-packages/mininet-2.3.0d1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/setuptools-32.1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/pip-9.0.1-py2.7.egg', '/home/wasdns/bmv2/mininet', '/usr/local/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PILcompat', '/usr/lib/python2.7/dist-packages/gtk-2.0', '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']

发现：'/home/wasdns/bmv2/mininet'，解决问题。