Python modules not installing correctly

Python modules not installing correctly

So, I downloaded Python 2.7.5 on Ubuntu 12.04 and attempted to install the
module "lxml" using:
sudo pip install lxml
When I try:
pip freeze
it lists lxml as an installed package, however when I run a python script
using
help('modules')
lxml is no longer listed amongst the modules. I've checked using
python -V
and I'm apparently running Python 2.7.5. I've done some poking around and
nothing seems to quite suite what's going on with me here. I believe that
I'm perhaps installing modules to a different version of Python, and
that's the reason pip lists it as installed but not Python's help command.
I'm rather new to Linux so I'm not particularly sure what to do next. Any
help is appreciated, thanks!