ImportError: No module named yaml

edit

After i recently installed a new version of python, nothing is working in ros. Every time i get import error saying no yaml found. For example, when i run roscore, i get an error as follows:

Traceback (most recent call last):

File "/opt/ros/diamondback/ros/bin/roscore", line 34, in <module>

from ros import roslaunch

File "/opt/ros/diamondback/ros/core/roslib/src/ros/__init__.py", line 41, in <module>

import roslib

File "/opt/ros/diamondback/ros/core/roslib/src/roslib/__init__.py", line 50, in <module>

from roslib.launcher import load_manifest

File "/opt/ros/diamondback/ros/core/roslib/src/roslib/launcher.py", line 45, in <module>

import roslib.manifest

File "/opt/ros/diamondback/ros/core/roslib/src/roslib/manifest.py", line 46, in <module>

import roslib.packages

File "/opt/ros/diamondback/ros/core/roslib/src/roslib/packages.py", line 58, in <module>

import roslib.os_detect

File "/opt/ros/diamondback/ros/core/roslib/src/roslib/os_detect.py", line 49, in <module>

import yaml

ImportError: No module named yaml

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And yes, i have installed yaml.

"sudo apt-get install python-yaml" gives

Reading package lists... Done

Building dependency tree

Reading state information... Done

python-yaml is already the newest version.

0 upgraded, 0 newly installed, 0 to remove and 107 not upgraded.

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What could be the problem?