python-dev无法安装

安装tensorflow之前需要先安装python—dev， 这个不能用pip install来安装，只能用sudo apt-get install来安装。安装后会发现还要先装另外两个东西，但是装这两个东西也还要继续装其他东西，相当麻烦且并没有成功

~$ sudo apt-get install python-dev
Reading package lists... Done
Building dependency tree       
Reading state information... Done
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.

用aptitude 工具可以搞定
先：sudo apt-get install aptitude
然后：
sudo aptitude install python-dev，之后会出现：

sudo aptitude install python-dev
The following NEW packages will be installed:
  libexpat1-dev{ab} libpython-dev{a} libpython2.7-dev{ab} python-dev 
  python2.7-dev{ab} 
0 packages upgraded, 5 newly installed, 0 to remove and 1 not upgraded.
Need to get 28.1 MB of archives. After unpacking 42.1 MB will be used.
The following packages have unmet dependencies:
 python2.7-dev : Depends: python2.7 (= 2.7.11-2) but 2.7.12-1ubuntu0~16.04.1 is installed.
                 Depends: libpython2.7 (= 2.7.11-2) but 2.7.12-1ubuntu0~16.04.1 is installed.
 libexpat1-dev : Depends: libexpat1 (= 2.1.0-7) but 2.1.0-7ubuntu0.16.04.2 is installed.
 libpython2.7-dev : Depends: libpython2.7-stdlib (= 2.7.11-2) but 2.7.12-1ubuntu0~16.04.1 is installed.
                    Depends: libpython2.7 (= 2.7.11-2) but 2.7.12-1ubuntu0~16.04.1 is installed.
open: 24; closed: 106; defer: 16; conflict: 21                                 .The following actions will resolve these dependencies:

     Keep the following packages at their current version:
1)     libexpat1-dev [Not Installed]                      
2)     libpython-dev [Not Installed]                      
3)     libpython2.7-dev [Not Installed]                   
4)     python-dev [Not Installed]                         
5)     python2.7-dev [Not Installed]                      



Accept this solution? [Y/n/q/?] n        这里一定要n，因为给的solution是保持现在的状态，即不安装
The following actions will resolve these dependencies:

     Downgrade the following packages:                                          
1)     libexpat1 [2.1.0-7ubuntu0.16.04.2 (now) -> 2.1.0-7 (xenial)]             
2)     libpython2.7 [2.7.12-1ubuntu0~16.04.1 (now) -> 2.7.11-2 (xenial)]        
3)     libpython2.7-minimal [2.7.12-1ubuntu0~16.04.1 (now) -> 2.7.11-2 (xenial)]
4)     libpython2.7-stdlib [2.7.12-1ubuntu0~16.04.1 (now) -> 2.7.11-2 (xenial)] 
5)     python2.7 [2.7.12-1ubuntu0~16.04.1 (now) -> 2.7.11-2 (xenial)]           
6)     python2.7-minimal [2.7.12-1ubuntu0~16.04.1 (now) -> 2.7.11-2 (xenial)]   



Accept this solution? [Y/n/q/?] y     接受新状态就可以安装了