Installation fails on apt-installed Sage

[bernalde]

When executing sage setup.py test I get the following error:

fgb_sage/_fgb_sage_int.pyx: cannot find cimported module 'sage.cpython.string'
Compiling fgb_sage/_fgb_sage_int.pyx because it changed.
[1/1] Cythonizing fgb_sage/_fgb_sage_int.pyx

Error compiling Cython file:
------------------------------------------------------------
...
# distutils: language = c++

# _fgb_int.pyx is source file,
# _fgb_modp.pyx is auto-generated!
from sage.cpython.string cimport str_to_bytes
^
------------------------------------------------------------

fgb_sage/_fgb_sage_int.pyx:5:0: 'sage/cpython/string.pxd' not found

Error compiling Cython file:
------------------------------------------------------------
...
# distutils: language = c++

# _fgb_int.pyx is source file,
# _fgb_modp.pyx is auto-generated!
from sage.cpython.string cimport str_to_bytes
^
------------------------------------------------------------

fgb_sage/_fgb_sage_int.pyx:5:0: 'sage/cpython/string/str_to_bytes.pxd' not found

Error compiling Cython file:
------------------------------------------------------------
...
        self.variables = <char**> PyMem_Malloc(self.n_variables * sizeof(char*))
        self.exponents = <I32*> PyMem_Malloc(self.n_variables * sizeof(I32*))
        if not self.input_basis or not self.output_basis or not self.variables or not self.exponents:
            raise MemoryError()

        self.pystr_variables = [str_to_bytes(x) for x in
                                           ^
------------------------------------------------------------

fgb_sage/_fgb_sage_int.pyx:146:44: 'str_to_bytes' is not a constant, variable or function identifier
Traceback (most recent call last):
  File "setup.py", line 156, in <module>
    for (name, libmode) in PYX_FILES]
  File "/usr/lib/python2.7/dist-packages/Cython/Build/Dependencies.py", line 1027, in cythonize
    cythonize_one(*args)
  File "/usr/lib/python2.7/dist-packages/Cython/Build/Dependencies.py", line 1149, in cythonize_one
    raise CompileError(None, pyx_file)
Cython.Compiler.Errors.CompileError: fgb_sage/_fgb_sage_int.pyx

I tried resolving it by myself but was not successful. I'm running an Ubuntu 18.04 machine with Sage v. 8.1 installed through apt-get.

[bernalde]

Resolved by reinstalling Sage. I first installed it through apt-get and now after using the binaries, it works.