Calling IPython from a virtualenv

You can force IPython to use a virtual environment if available by adding file below to ~/.ipython/profile_default/startups:

import os
import sys

if 'VIRTUAL_ENV' in os.environ:
    py_version = sys.version_info[:2] # formatted as X.Y 
    py_infix = os.path.join('lib', ('python%d.%d' % py_version))
    virtual_site = os.path.join(os.environ.get('VIRTUAL_ENV'), py_infix, 'site-packages')
    dist_site = os.path.join('/usr', py_infix, 'dist-packages')

    # OPTIONAL: exclude debian-based system distributions sites
    sys.path = filter(lambda p: not p.startswith(dist_site), sys.path)

    # add virtualenv site
    sys.path.insert(0, virtual_site)

I recommend naming it 00-virtualenv.py so changes will be made as early as possible.

Note: Make sure ipython is installed in the new virtual environment to get this to work.

As others mentioned, recent versions of ipython are virtualenv aware, so you can use your virtualenv bin activate script to run ipython using your virtualenv, e.g.

$ source venv/bin/activate
(venv) $ ipython
WARNING: Attempting to work in a virtualenv. If you encounter problems, please install IPython inside the virtualenv.

If you’re trying to open a notebook, even ipython 5 won’t help – ipython will disregard the virtualenv (at least on my machine/setup).
You’ll need to use rgtk’s script, but please make sure to modify the optional filter part and the sys.path.insert as below:

import os
import sys

if 'VIRTUAL_ENV' in os.environ:
    py_version = sys.version_info[:2] # formatted as X.Y 
    py_infix = os.path.join('lib', ('python%d.%d' % py_version))
    virtual_site = os.path.join(os.environ.get('VIRTUAL_ENV'), py_infix, 'site-packages')
    dist_site = os.path.join('/usr', py_infix, 'dist-packages')

    # OPTIONAL: exclude debian-based system distributions sites
    # ADD1: sys.path must be a list
    sys.path = list(filter(lambda p: not p.startswith(dist_site), sys.path))

    # add virtualenv site
    # ADD2: insert(0 is wrong and breaks conformance of sys.path
    sys.path.insert(1, virtual_site)

• ADD1: in the original script we get back a filter object, we would break sys.path and insert below would fail
• ADD2: see this question and python documentation

(Debian/Ubuntu) assuming some version (x) of Python3 is installed, then:

$ sudo apt-get install -y ipython
$ virtualenv --python=python3.x .venv
$ source .venv/bin/activate
$ pip3 install ipython
$ ipython3

will launch ipython running your version of Python3.

The answer given by @SiddharthaRT is good! Following this approach, it is simpler for me just:

python -m IPython

This will use the module IPython through the python bin, ensuring that it refers to the bin from the virtual env.

1. Activate your virtual environment by using source ~/.virtualenvs/my_venv/bin/activate or by running workon my_venv
   (Depending on how you’ve installed the my_venv virtual environment)

2. Install ipython

pip install ipython

3. Now run ipython from my_venv.

If it still loads the system’s ipython, then run hash -r in your shell

This will reset the cache of your shell and ensure you don’t run another ipython that was already called in this shell session.

I’ll chime in years later in hopes someone finds this useful.

This solution solves a few problems:

• You don’t need iPython installed in the current virtualenv, only for the global Python that matches your virtualenv’s Python version (3.6 != 3.7).
• Works for users of pyenv where your global Python version might be 3.7 and your local virtualenv Python is 3.6 therefore using the global ipython will fail.
• Works outside of virtual environments (though not particularly useful as it always targets python).

Throw this in your ~/.bashrc or ~/.zshrc or what have you:

# This is a roundabout way to start ipython from inside a virtualenv without it being installed
# in that virtualenv. The only caveot is that the "global" python must have ipython installed.
# What this function does that's different than simply calling the global ipython is it ensures to
# call the ipython that is installed for the same major.minor python version as in the virtualenv.
# This is most useful if you use pyenv for example as global python3 could be 3.7 and local
# virtualenv python3 is 3.6.
function ipy {
  local PY_BIN
  local IPYTHON
  local PYV
  # This quick way will work if ipython is in the virtualenv
  PY_BIN="$(python -c 'import sys; print(sys.executable)')"
  IPYTHON="$(dirname "$PY_BIN")/ipython"
  if [[ -x "$IPYTHON" ]]; then
    "$IPYTHON"
  else
    # Ask the current python what version it is
    PYV="$(python -c 'import sys; print(".".join(str(i) for i in sys.version_info[:2]))')"
    echo "Looking for iPython for Python $PYV"
    # In a new shell (where pyenv should load if equipped) try to find that version
    PY_BIN="$($SHELL -i -c "python$PYV -c 'import sys; print(sys.executable)'")"
    "$(dirname "$PY_BIN")/ipython"
  fi
}

Then source or open a new terminal and run ipy.