title: ubuntu /usr/bin/env: python: No such file or directory
body: <p>I update the kernel, after that the Ubuntu doesn't work well, PS: I try to exec "meld" command, it will report that "/usr/bin/env: python: No such file or directory", 
  then I exec "sudo apt-get install python" and get the result "python is already the newest version.", what should I do for it.</p>
  
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  <p>I'm not good at linux, can you tell me how to revert my linux to the last right status, or reinstall the python normally.</p>