matplotlib - 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 :)