Setting macosx as the default backend causes an ImportError

[ngoldbaum]

In matplotlib 3.0.0 or newer, the build setting the macosx backend as the default backend for the wheel build of matplotlib causes an ImportError:

○ python test.py --verbose-debug
$HOME=/Users/goldbaum
CONFIGDIR=/Users/goldbaum/.matplotlib
matplotlib data path: /Users/goldbaum/.pyenv/versions/3.6.5/lib/python3.6/site-packages/matplotlib/mpl-data
loaded rc file /Users/goldbaum/.pyenv/versions/3.6.5/lib/python3.6/site-packages/matplotlib/mpl-data/matplotlibrc
matplotlib version 3.0.2
interactive is False
platform is darwin
loaded modules: ['builtins', 'sys', '_frozen_importlib', '_imp', '_warnings', '_thread', '_weakref', '_frozen_importlib_external', '_io', 'marshal', 'posix', 'zipimport', 'encodings', 'codecs', '_codecs', 'encodings.aliases', 'encodings.utf_8', '_signal', '__main__', 'encodings.latin_1', 'io', 'abc', '_weakrefset', 'site', 'os', 'errno', 'stat', '_stat', 'posixpath', 'genericpath', 'os.path', '_collections_abc', '_sitebuiltins', 'sysconfig', '_sysconfigdata_m_darwin_darwin', '_osx_support', 're', 'enum', 'types', 'functools', '_functools', 'collections', 'operator', '_operator', 'keyword', 'heapq', '_heapq', 'itertools', 'reprlib', '_collections', 'weakref', 'collections.abc', 'sre_compile', '_sre', 'sre_parse', 'sre_constants', '_locale', 'copyreg', '_bootlocale', 'importlib', 'importlib._bootstrap', 'importlib._bootstrap_external', 'warnings', 'importlib.util', 'importlib.abc', 'importlib.machinery', 'contextlib', 'mpl_toolkits', 'matplotlib', 'atexit', 'distutils', 'distutils.version', 'inspect', 'ast', '_ast', 'dis', 'opcode', '_opcode', 'linecache', 'tokenize', 'token', 'locale', 'logging', 'time', 'traceback', 'string', '_string', 'threading', 'pathlib', 'fnmatch', 'ntpath', 'urllib', 'urllib.parse', 'pprint', 'shutil', 'zlib', 'bz2', '_compression', '_bz2', 'lzma', '_lzma', 'pwd', 'grp', 'subprocess', 'signal', '_posixsubprocess', 'select', 'selectors', 'math', 'tempfile', 'random', 'hashlib', '_hashlib', '_blake2', '_sha3', 'bisect', '_bisect', '_random', 'urllib.request', 'base64', 'struct', '_struct', 'binascii', 'email', 'http', 'http.client', 'email.parser', 'email.feedparser', 'email.errors', 'email._policybase', 'email.header', 'email.quoprimime', 'email.base64mime', 'email.charset', 'email.encoders', 'quopri', 'email.utils', 'socket', '_socket', 'datetime', '_datetime', 'email._parseaddr', 'calendar', 'email.message', 'uu', 'email._encoded_words', 'email.iterators', 'ssl', 'ipaddress', 'textwrap', '_ssl', 'urllib.error', 'urllib.response', '_scproxy', 'matplotlib.cbook', 'glob', 'gzip', 'numbers', 'numpy', '__future__', 'numpy._globals', 'numpy.__config__', 'numpy.version', 'numpy._import_tools', 'numpy.add_newdocs', 'numpy.lib', 'numpy.lib.info', 'numpy.lib.type_check', 'numpy.core', 'numpy.core.info', 'numpy.core.multiarray', 'numpy.core.umath', 'numpy.core._internal', 'numpy.compat', 'numpy.compat._inspect', 'numpy.compat.py3k', 'ctypes', '_ctypes', 'ctypes._endian', 'numpy.core.numerictypes', 'numpy.core.numeric', 'pickle', '_compat_pickle', '_pickle', 'numpy.core.fromnumeric', 'numpy.core._methods', 'numpy.core.arrayprint', 'numpy.core.defchararray', 'numpy.core.records', 'numpy.core.memmap', 'numpy.core.function_base', 'numpy.core.machar', 'numpy.core.getlimits', 'numpy.core.shape_base', 'numpy.core.einsumfunc', 'numpy.testing', 'unittest', 'unittest.result', 'unittest.util', 'unittest.case', 'difflib', 'unittest.suite', 'unittest.loader', 'unittest.main', 'argparse', 'copy', 'gettext', 'unittest.runner', 'unittest.signals', 'numpy.testing._private', 'numpy.testing._private.utils', 'gc', 'numpy.lib.utils', 'numpy.testing._private.decorators', 'numpy.testing._private.nosetester', 'numpy.testing._private.pytesttester', 'numpy.lib.ufunclike', 'numpy.lib.index_tricks', 'numpy.lib.function_base', 'numpy.lib.twodim_base', 'numpy.lib.histograms', 'numpy.matrixlib', 'numpy.matrixlib.defmatrix', 'numpy.linalg', 'numpy.linalg.info', 'numpy.linalg.linalg', 'numpy.linalg.lapack_lite', 'numpy.linalg._umath_linalg', 'numpy.lib.stride_tricks', 'numpy.lib.mixins', 'numpy.lib.nanfunctions', 'numpy.lib.shape_base', 'numpy.lib.scimath', 'numpy.lib.polynomial', 'numpy.lib.arraysetops', 'numpy.lib.npyio', 'numpy.lib.format', 'numpy.lib._datasource', 'numpy.lib._iotools', 'numpy.lib.financial', 'decimal', '_decimal', 'numpy.lib.arrayterator', 'numpy.lib.arraypad', 'numpy.lib._version', 'numpy.core._multiarray_tests', 'numpy._distributor_init', 'numpy.fft', 'numpy.fft.info', 'numpy.fft.fftpack', 'numpy.fft.fftpack_lite', 'numpy.fft.helper', 'numpy.polynomial', 'numpy.polynomial.polynomial', 'numpy.polynomial.polyutils', 'numpy.polynomial._polybase', 'numpy.polynomial.chebyshev', 'numpy.polynomial.legendre', 'numpy.polynomial.hermite', 'numpy.polynomial.hermite_e', 'numpy.polynomial.laguerre', 'numpy.random', 'numpy.random.info', 'cython_runtime', 'mtrand', 'numpy.random.mtrand', 'numpy.ctypeslib', 'numpy.ma', 'numpy.ma.core', 'numpy.ma.extras', 'matplotlib.cbook.deprecation', 'matplotlib.rcsetup', 'matplotlib.fontconfig_pattern', 'pyparsing', 'matplotlib.colors', 'matplotlib._color_data', 'cycler', 'six', 'six.moves', 'matplotlib._version', 'json', 'json.decoder', 'json.scanner', '_json', 'json.encoder', 'dateutil', 'dateutil._version']
CACHEDIR=/Users/goldbaum/.matplotlib
Using fontManager instance from /Users/goldbaum/.matplotlib/fontlist-v300.json
Traceback (most recent call last):
  File "test.py", line 1, in <module>
    from matplotlib import pyplot
  File "/Users/goldbaum/.pyenv/versions/3.6.5/lib/python3.6/site-packages/matplotlib/pyplot.py", line 2374, in <module>
    switch_backend(rcParams["backend"])
  File "/Users/goldbaum/.pyenv/versions/3.6.5/lib/python3.6/site-packages/matplotlib/pyplot.py", line 207, in switch_backend
    backend_mod = importlib.import_module(backend_name)
  File "/Users/goldbaum/.pyenv/versions/3.6.5/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/Users/goldbaum/.pyenv/versions/3.6.5/lib/python3.6/site-packages/matplotlib/backends/backend_macosx.py", line 14, in <module>
    from matplotlib.backends import _macosx
ImportError: Python is not installed as a framework. The Mac OS X backend will not be able to function correctly if Python is not installed as a framework. See the Python documentation for more information on installing Python as a framework on Mac OS X. Please either reinstall Python as a framework, or try one of the other backends. If you are using (Ana)Conda please install python.app and replace the use of 'python' with 'pythonw'. See 'Working with Matplotlib on OSX' in the Matplotlib FAQ for more information.

This could be fixed by not setting macosx as the default backend in the matplotlibrc that gets shipped with the wheel.

[jklymak]

The behaviour in Matplotlib changed in matplotlib/matplotlib#11600 Before it'd fallback on agg, not it fails to fallback...

[tacaswell]

This appears to be fixed.