The following packages have unmet dependencies

Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 python-dev : Depends: libpython-dev (= 2.7.11-1) but it is not going to be installed
              Depends: python2.7-dev (>= 2.7.11-1~) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.


解决办法aptitude命令代替apt-get命令
apt-get install aptitude
aptitude install  python-dev


The following packages have unmet dependencies:
Keep the following packages at their current version:                  
Accept this solution? [Y/n/q/?]
这个命令会正对冲突做解决依赖，会先询问冲突的包版本是否要保留，我们选n不保留，
然后会下一步问我们这些包依赖要安装是否接受，选Y.即可完美解决这个问题。