Python 3: Installing gi package with pip

Question

I am trying to run this Matplotlib example using Python 3. To run this I needed to install gi first (I am using pyenv):

$ python --version
Python 3.6.1
$ pip --version
pip 9.0.1 from /home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages (python 3.6)
$ pip install gi
Collecting gi
  Downloading gi-1.2.tar.gz
Collecting requests (from gi)
  Downloading requests-2.16.0-py2.py3-none-any.whl (85kB)
    100% |████████████████████████████████| 92kB 959kB/s 
Collecting idna<2.6,>=2.5 (from requests->gi)
  Downloading idna-2.5-py2.py3-none-any.whl (55kB)
    100% |████████████████████████████████| 61kB 1.2MB/s 
Collecting chardet<3.1.0,>=3.0.2 (from requests->gi)
  Downloading chardet-3.0.3-py2.py3-none-any.whl (133kB)
    100% |████████████████████████████████| 143kB 1.8MB/s 
Collecting urllib3<1.22,>=1.21.1 (from requests->gi)
  Downloading urllib3-1.21.1-py2.py3-none-any.whl (131kB)
    100% |████████████████████████████████| 133kB 1.8MB/s 
Collecting certifi>=2017.4.17 (from requests->gi)
  Downloading certifi-2017.4.17-py2.py3-none-any.whl (375kB)
    100% |████████████████████████████████| 378kB 284kB/s 
Installing collected packages: idna, chardet, urllib3, certifi, requests, gi
  Running setup.py install for gi ... done
Successfully installed certifi-2017.4.17 chardet-3.0.3 gi-1.2 idna-2.5 requests-2.16.0 urllib3-1.21.1

Now, running the example:

$ python toolmanager.py 
Traceback (most recent call last):
  File "./toolmanager.py", line 8, in <module>
    import matplotlib.pyplot as plt
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/pyplot.py", line 115, in <module>
    _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/backends/__init__.py", line 32, in pylab_setup
    globals(),locals(),[backend_name],0)
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/backends/backend_gtk3cairo.py", line 6, in <module>
    from . import backend_gtk3
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/backends/backend_gtk3.py", line 10, in <module>
    import gi
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/gi/__init__.py", line 39
    print url
            ^
SyntaxError: Missing parentheses in call to 'print'

Seems like pip somehow installed a Python 2 version? How can I fix this?

Answer 1

First, pip install gi will install another unrelated package, the correct name is pgi. But after running:

$ pip uninstall gi
$ pip install pgi
$ python toolmanager.py
[...]
Traceback (most recent call last):
  File "toolmanager.py", line 14, in <module>
    import matplotlib.pyplot as plt
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/pyplot.py", line 115, in <module>
    _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/backends/__init__.py", line 32, in pylab_setup
    globals(),locals(),[backend_name],0)
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/backends/backend_gtk3cairo.py", line 6, in <module>
    from . import backend_gtk3
  File "/home/hakon/.pyenv/versions/3.6.1/lib/python3.6/site-packages/matplotlib/backends/backend_gtk3.py", line 12, in <module>
    raise ImportError("Gtk3 backend requires pygobject to be installed.")
ImportError: Gtk3 backend requires pygobject to be installed.

It seems that pygobject for Python 3 cannot be installed from PyPI. So I tried to install everything from the Ubuntu distribution package python3-gi instead:

$ sudo apt-get install python3-gi
$ pyenv local system
$ python3 --version
Python 3.5.3
$ python3 toolmanager.py

and this works fine :)

Answer 2

To install for the standard python, Håkon Hægland answer is the best choice.

But for an alternate python version, one can use pip<version>. Beware that the alternate pip has to be used to match the alternate python.

The full explanations are given in the documentation.

For instance on openSUSE (standard python version 3.6, alternate installed 3.8):

> sudo zypper install cairo-devel pkg-config python3-devel gcc gobject-introspection-devel
> pip3.8 install --user pycairo
> pip3.8 install --user PyGObject
> python3.8
Python 3.8.1 (default, Feb  1 2020, 14:50:41) 
[GCC 7.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import gi
>>>