Python: Installing PIP and Virtualenv without root

Using virtualenv in combination with pip is a great way to run isolated python environments with all kinds of packages. However if the system you are using does not have pip, easy_install or virtualenv installed system-wide, it’s a little bit tricky to set up.

With some experimentation and some googling (stackoverflow), here’s a quick guide to do it. I’m assuming you have python already on the system.

First, we need ez_setup. The following commands grab the scripts and install them to ~/.local/bin:

python –-user

Now we can install pip in the same way:

curl -O
python –-user

Now we have pip, and just need to add it to the path variable (add it to your .bashrc):

export PATH=~/.local/bin:$PATH

Finally, we can install packages. Get virtualenv:

pip install --user virtualenv

Now you can set up virtual environments for python, which is well-documented here.

Neat Python Debugging Trick

Debugging python is a pretty painless experience using pdb, the built in standard debugger. The basic usage is to insert breakpoints in the code:

import pdb

print('hello world')
print('entering breakpoint')
sum = 0
for x in range(0, 10):
    sum += x

When the interpreter hits ‘pdb.set_trace()’ it’ll launch the interactive debugging interface, which lets you investigate the different variables, print things and run calculations. A tutorial on using pdb can be found here.

A really useful trick using this snippet allows for quick debugging anywhere in your code. Place the following lines at the top of your python script:

import signal
    def int_handler(signal, frame):
       import pdb
signal.signal(signal.SIGINT, int_handler)
Then run the script, and wherever you want to start a debugger press ‘ctrl’+’c’. Press ‘c’ to carry on with execution. Really useful for unpredictable bugs!