最近在尝试用python写爬虫，需要用到requests模块，却安装不上。
系统ubuntu16.04, 使用系统默认的python2.7. 运行python代码时，报错：
p@G :~/Desktop$ sudo apt-get install python-requests
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies.
bcloud : Depends: python3-crypto but it is not going to be installed

      Depends: python3-pyinotify but it is not going to be installed
      Depends: python3-keyring but it is not going to be installed

python-requests : Depends: python-urllib3 (>= 1.13.1) but it is not going to be installed

               Depends: python-chardet but it is not going to be installed
               Depends: python-urllib3 (< 1.13.2) but it is not going to be installed

E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

尝试更新软件源，未解决。
尝试安装python3-crypto等模块，未解决。
百度说，可能是PPA版本问题，但未安装和删除过PPA.
这是什么问题？
Any help will be welcomed!!