matplotlib for Py3

[jrkerns]

matplotlib seems to be installed for the RTD python 2.x interpreter, but not for 3.x. Is this accurate? Can we get matplotlib for the python 3 interpreter? Thanks!

Py3 output: https://readthedocs.org/builds/pylinac/2140306/ (no matplotlib)
Py2 output: https://readthedocs.org/builds/pylinac/2140221/ (build chokes on py3 code, but has found matplotlib)

[ankostis]

Related bugs: #896, #1056

[cdeil]

We have a Python 3 only package that uses matplotlib for the docs.
Currently we have matplotlib listed in
https://github.com/cta-observatory/ctapipe/blob/master/docs/rtd-pip-requirements
Is that the right thing to do or should we remove it because matplotlib is available system-wide for Python 3?

Build error:
https://readthedocs.org/builds/ctapipe/3001202/

Collecting matplotlib (from -r docs/rtd-pip-requirements (line 2))
  Using cached matplotlib-1.4.3.tar.gz
    Complete output from command python setup.py egg_info:
    IMPORTANT WARNING:
        pkg-config is not installed.
        matplotlib may not be able to find some of its dependencies
    ============================================================================
    Edit setup.cfg to change the build options

    BUILDING MATPLOTLIB
                matplotlib: yes [1.4.3]
                    python: yes [3.4.0 (default, Apr 11 2014, 13:05:11)  [GCC
                            4.8.2]]
                  platform: yes [linux]

    REQUIRED DEPENDENCIES AND EXTENSIONS
                     numpy: yes [not found. pip may install it below.]
                       six: yes [using six version 1.9.0]
                  dateutil: yes [dateutil was not found. It is required for date
                            axis support. pip/easy_install may attempt to
                            install it after matplotlib.]
                      pytz: yes [using pytz version 2015.4]
                   tornado: yes [using tornado version 4.2]
                 pyparsing: yes [pyparsing was not found. It is required for
                            mathtext support. pip/easy_install may attempt to
                            install it after matplotlib.]
                     pycxx: yes [Official versions of PyCXX are not compatible
                            with matplotlib on Python 3.x, since they lack
                            support for the buffer object.  Using local copy]
                    libagg: yes [pkg-config information for 'libagg' could not
                            be found. Using local copy.]
    Traceback (most recent call last):
      File "<string>", line 20, in <module>
      File "/tmp/pip-build-v2u7hzf0/matplotlib/setup.py", line 155, in <module>
        result = package.check()
      File "/tmp/pip-build-v2u7hzf0/matplotlib/setupext.py", line 961, in check
        min_version='2.3', version=version)
      File "/tmp/pip-build-v2u7hzf0/matplotlib/setupext.py", line 445, in _check_for_pkg_config
        if (not is_min_version(version, min_version)):
      File "/tmp/pip-build-v2u7hzf0/matplotlib/setupext.py", line 173, in is_min_version
        return found_version >= expected_version
      File "/usr/lib/python3.4/distutils/version.py", line 76, in __ge__
        c = self._cmp(other)
      File "/usr/lib/python3.4/distutils/version.py", line 343, in _cmp
        if self.version < other.version:
    TypeError: unorderable types: str() < int()

[gregmuellegger]

@cdeil The safest bet here is to remove the matplotlib dependency from the requirements file and mock out the library for the build like explained in the FAQs.

[cdeil]

We're using the matplotlib Sphinx plot directive to generate Figures during the Sphinx build.
So if we mock out matplotlib, those Figures will not be generated and the docs are incomplete.

[gregmuellegger]

@cdeil oops, completely missed that. Removing matplotlib from the requirements and activating the "use system site packages" switch in the admin panel on readthedocs.org should make it work then -- as long as matplotlib is installed for Python 3. Which is not currently.

We'll fix that!

[ankostis]

@cdeil When you fix it, update also #896.

[gregmuellegger]

This is finally fixed on our build servers. You can use matplotlib in Python 3 projects now. Thanks for the report and persistence!