unable to install any module with pip without doing sudo

Question

I am not able to install any module with pip unless I do it with sudo. Below is error trace.

LAP:models$ pip install -U scikit-learn
Traceback (most recent call last):
  File "/usr/local/bin/pip", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 2793, in <module>
    working_set.require(__requires__)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 673, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 576, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: pip==8.0.3

I looked online but did not find any solution so far.