I wanted to use iPython Notebook in Python 3 on Ubuntu 14.04. Because I have both Python 2.7 and Python 3.4 installed on my system--and for other implementation-specific reasons--I decided to use a Python virtual environment (with virtualenv). Very little has been written about this topic so far...

These reports don't specifically handle Python 3 and virtual environments. Furthermore, the the official and various unofficial guides to installing iPython Notebook don't deal with this use case, either.

The main problem I encountered is with the ZMQ library. To install the library and the Python bindings system-wide I used apt-get:

sudo apt-get install libzmq3 libzmq3-dev python3-zmq

But when I tried pip install ipython[notebook], either inside or outside my virtualenv, the installation would fail with exit status 1 and the warnings:

Warning: Detected ZMQ version: 4.0.4, but pyzmq targets ZMQ 4.0.5.
Warning: libzmq features and fixes introduced after 4.0.4 will be unavailable.

I confirmed in Synaptic Package Manager that the libzmq3 package for Ubuntu is only version 4.0.4. As an alternative, I tried this fix, having pyzmq build its own libzmq dependency:

 pip install pyzmq --install-option="--zmq=bundled"

But this failed because it couldn't find a certain header file:

    buildutils/initlibsodium.c:10:20: fatal error: Python.h: No such file or directory
 #include "Python.h"
compilation terminated.
error: command 'x86_64-linux-gnu-gcc' failed with exit status 1

Next, I built libzmq version 4.0.5 from source.

wget http://download.zeromq.org/zeromq-4.0.5.tar.gz
tar -xzvf zeromq-4.0.5.tar.gz && rm zeromq-4.0.5.tar.gz
cd /usr/local/zmq/zeromq-4.0.5
make -j 6
sudo make install

No problems encountered. After this, I tried to install pyzmq in my virtual environment with:

easy_install pyzmq

I also tried building pyzmq from source. In both cases, I could see from the output that the proper ZMQ version (4.0.5) was detected, but the installation failed because I didn't have Cython installed (a not-well-documented dependency for building pyzmq, in my opinion).

After installing Cython for Python 3...

sudo apt-get install cython3

I tried installing pyzmq again with pip and with easy_install both inside and outside the virtual environment; it still didn't work. This message was delivered despite cython3 being installed:

Fatal: Cython-generated file 'zmq/backend/cython/_device.c' not found.
            Cython >= 0.16 is required to compile pyzmq from a development branch.
            Please install Cython or download a release package of pyzmq.

And this file structure:

$ ls -l zmq/backend/cython/
checkrc.pxd         context.pxd         __init__.py         _poll.pyx           utils.pxd           
constant_enums.pxi  context.pyx         libzmq.pxd          rebuffer.pyx        utils.pyx           
constants.pxi       _device.pyx         message.pxd         socket.pxd          _version.pyx        
constants.pyx       error.pyx           message.pyx         socket.pyx 

2 Answers 2


The "Python.h" error message indicates that you are missing the python3-devpackage, which you need to build any Python extensions (Python modules written in C), which you can get with:

apt-get install python3-dev

To get up and running from scratch:

apt-get update && apt-get install python3-dev python3-pip build-essential libzmq3-dev
pip3 install virtualenv
virtualenv -p $(which python3) myenv
source myenv/bin/activate
pip install pyzmq
python -c 'import zmq; print(zmq.zmq_version())'
# 4.0.4

The installed packages:

  • build-essential: compilers and headers for building things on Ubuntu.
  • python3-dev: headers (Python.h) needed for compiling any Python extensions.
  • libzmq3-dev: the libzmq library and its headers. This is optional, but recommended. PyZMQ will link against libzmq found on the system if it can, otherwise it will build libzmq itself as a Python extension.
  • pip, virtualenv: Shouldn't be needed, but used to workaround Ubuntu's bug that breaks python3 -m venv.

I ran the above commands in a base ubuntu:14.04 docker container to verify that they are sufficient to successfully build pyzmq in a virtualenv.

  • Thanks for looking into this. I'm aware of the -dev family of packages so I'm pretty sure I would have had it installed at the time (I just checked and I currently do). At any rate, my particular problem seemed to hinge, at the time, on using the correct implementation of pip (pip for Python 3).
    – Arthur
    May 21, 2015 at 18:00
  • Missing Python.h means you didn't have the Python headers at compile time. It's possible you had python-dev but not python3-dev when you ran it. I would be interested to hear if you still have this problem running the install after knowing you have python3-dev.
    – minrk
    May 22, 2015 at 20:41
  • If you are in a virtualenv pip always corresponds to the version in the env. You never need to use pipX in a virtualenv, and further probably shouldn't because it's the easiest way to get out of your env by accident (e.g. pip3.4 in a Python 3.3 env will work, but will install outside the env, whereas pip will always install in the active env). pipX should only be used when you are not using envs.
    – minrk
    May 22, 2015 at 20:42

Finally, I considered installing iPython Notebook system-wide (outside a virtual environment). I had previously tried just install pyzmq system-wide but this wasn't enough.

When I considered install iPython Notebook outside the virtual environment, I realized, "How do I get pip to discriminate between Python 2.7 and Python 3.4?" I went searching and found this excellent answer. In fact, it turns out my central problem was related to pip. I installed the pip corresponding to my Python 3 version:

sudo apt-get install python3-setuptools
sudo easy_install3 pip

And after that, installing both pyzmq and ipython[notebook] worked perfectly inside my virtual environment:

pip3.4 install pyzmq
pip install ipython[notebook]

I accidently used pip instead of pip3.4 for ipython[notebook] but it works anyway:

(my-virtual-env)me@computer:~$ pip freeze

However, using pip3.4 was necessary to get pyzmq installed in a Python 3 virtual environment.

  • And to get iPython Notebook running, instead of ipython notebook use ipython3 notebook.
    – Arthur
    Jan 15, 2015 at 17:16

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