How do I install python3-gi within virtualenv?

Update 2018 – Debian Stretch

1. Install GTK+ 3 / GIR.

   apt install libcairo2-dev libgirepository1.0-dev gir1.2-gtk-3.0
   

2. Create a virtual environment.

   python3 -mvenv venv
   

3. Install pygobject (pycairo should come as a dependency).

   venv/bin/pip install pygobject
   

Update 2018 – macOS

1. Install GTK+ 3 and Gobject Introspection with Homebrew.

   brew install gtk+3 gobject-introspection
   

2. Create and activate a virtual environment.

   python3 -mvenv venv
   

3. Install pygobject (pycairo should come as a dependency).

   PKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfig ARCHFLAGS="-arch x86_64" venv/bin/pip install pygobject
   

Original answer

This is what I did to get GTK+ 3 within a Python 3.5 virtual environment on OS X 10.11.

1. Install GTK+ 3 with Homebrew.

   brew install gtk+3
   

2. Create and activate a virtual environment.

   pyvenv-3.5 venv
   source venv/bin/activate
   cd venv
   

3. Install pycairo on the virtual environment.

   export PKG_CONFIG_PATH=$VIRTUAL_ENV/lib/pkgconfig
   
   curl -L https://cairographics.org/releases/pycairo-1.10.0.tar.bz2 | tar xj
   cd pycairo-1.10.0
   export ARCHFLAGS='-arch x86_64'
   
   python waf configure --prefix=$VIRTUAL_ENV # It's ok, this will fail.
   sed -i '' '154s/data={}/return/' .waf3-1.6.4-*/waflib/Build.py # Bugfix: https://bugs.freedesktop.org/show_bug.cgi?id=76759
   python waf configure --prefix=$VIRTUAL_ENV # Now it should configure.
   python waf build
   python waf install
   
   unset ARCHFLAGS
   cd ..
   

4. Install pygobject on the virtual environment.

   export PKG_CONFIG_PATH=$VIRTUAL_ENV/lib/pkgconfig:/usr/local/opt/libffi/lib/pkgconfig
   
   curl -L http://ftp.gnome.org/pub/GNOME/sources/pygobject/3.12/pygobject-3.12.2.tar.xz | tar xJ
   cd pygobject-3.12.2
   
   ./configure CFLAGS="-I$VIRTUAL_ENV/include" --prefix=$VIRTUAL_ENV
   make
   make install
   
   cd ..
   

5. Profit.

   Python 3.5.1 (v3.5.1:37a07cee5969, Dec  5 2015, 21:12:44)
   [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
   Type "help", "copyright", "credits" or "license" for more information.
   >>> from gi.repository import Gtk, Gdk, Pango, GObject
   >>> from cairo import ImageSurface, Context, FORMAT_ARGB32
   >>>
   

Python 3.5 downloaded and installed from PSF.

I haven't found a proper solution to this. When I run into situations where I can't get something to install into a virtualenv directly, I symlink it there and it works fine (there are probably exceptions, but this is not one of them).

ln -s /usr/lib/python3/dist-packages/gi /path_to_venv/lib/python3.4/site-packages/

Not elegant in the slightest; seems nicer than giving the virtualenv full access to all system packages though (via --system-site-packages).

The pip package name is somewhat counterintuitive - use pip install PyGObject.

It is now possible to resolve this using vext. Vext allows you to install packages in a virtualenv that individually access your system packages. To access gi, do the following:

pip install vext
pip install vext.gi