cython: Cython 0.29 cannot import 'pythran_is_numpy_func_supported'

After installing Cython 0.29 I was unable to run the line:

from Cython.Build.Inline import _get_build_extension

The full error message is below. It appears, for example, when calling pystan.

<ipython-input-4-468ee6613710> in <module>()
----> 1 import pystan
      2 overwrite=False
      3 nocov = '''
      4 functions {
      5     real bailerjones_lpdf(real r, real L){             //This is our distance prior

~/.local/lib/python3.6/site-packages/pystan/__init__.py in <module>()
      7 import logging
      8 
----> 9 from pystan.api import stanc, stan
     10 from pystan.misc import read_rdump, stan_rdump, stansummary
     11 from pystan.diagnostics import check_hmc_diagnostics

~/.local/lib/python3.6/site-packages/pystan/api.py in <module>()
     14 import pystan._api  # stanc wrapper
     15 from pystan._compat import string_types, PY2
---> 16 from pystan.model import StanModel
     17 
     18 logger = logging.getLogger('pystan')

~/.local/lib/python3.6/site-packages/pystan/model.py in <module>()
     30 
     31 import Cython
---> 32 from Cython.Build.Inline import _get_build_extension
     33 from Cython.Build.Dependencies import cythonize
     34 

~/.local/lib/python3.6/site-packages/Cython/Build/Inline.py in <module>()
     15 from ..Compiler.Main import Context, CompilationOptions, default_options
     16 
---> 17 from ..Compiler.ParseTreeTransforms import (CythonTransform,
     18         SkipDeclarations, AnalyseDeclarationsTransform, EnvTransform)
     19 from ..Compiler.TreeFragment import parse_from_strings

~/.local/lib/python3.6/site-packages/Cython/Compiler/ParseTreeTransforms.py in <module>()
     12 from . import PyrexTypes
     13 from . import Naming
---> 14 from . import ExprNodes
     15 from . import Nodes
     16 from . import Options

~/.local/lib/python3.6/site-packages/Cython/Compiler/ExprNodes.py in <module>()
     44 from .DebugFlags import debug_disposal_code, debug_temp_alloc, \
     45     debug_coercion
---> 46 from .Pythran import (to_pythran, is_pythran_supported_type, is_pythran_supported_operation_type,
     47      is_pythran_expr, pythran_func_type, pythran_binop_type, pythran_unaryop_type, has_np_pythran,
     48      pythran_indexing_code, pythran_indexing_type, is_pythran_supported_node_or_none, pythran_type,

ImportError: cannot import name 'pythran_is_numpy_func_supported'

I also received the error message when attempting the following from commandline:

pip3 install cftime --user.

This has been resolved since reverting to version 0.28.5.

I am using Ubuntu 18.04 and Python 3.6.6.