Xgboost: pip install not working under ububtu 14.04

[hectoraus]

gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.1) 
r@ubuntu:~$ sudo pip install xgboost
Downloading/unpacking xgboost
  Could not find a version that satisfies the requirement xgboost (from versions: 0.4a12, 0.4a13, 0.4a14, 0.4a15, 0.4a18, 0.4a19, 0.4a20, 0.4a21, 0.4a22, 0.4a23, 0.4a24, 0.4a25, 0.4a26, 0.4a27, 0.4a28, 0.4a29, 0.4a30)
Cleaning up...
No distributions matching the version for xgboost
Storing debug log for failure in /home/r/.pip/pip.log

I was able to install it a few weeks ago, but I don't remember how.
I already installed gcc

[phunterlau]

the system python's pip needs --pre parameter for having these 0.4a pre-releases.

[hectoraus]

it worked, thanks!!