Trac #26403: Compile Sage with Cython language_level=3str

Cython 0.29 introduces a new `language_level=3str`, which is like
`language_level=3` except that strings are still `str` instead of
`unicode`. It would be good to use this language_level in Sage to force
Python 3 syntax in all Cython files.

URL: https://trac.sagemath.org/26403
Reported by: jdemeyer
Ticket author(s): Jeroen Demeyer
Reviewer(s): Frédéric Chapoton

Author: Release Manager

src/sage/algebras/letterplace/free_algebra_element_letterplace.pyx

@@ -15,7 +15,6 @@ AUTHOR:
 - Simon King (2011-03-23): Trac ticket :trac:`7797`
 
 """
-from __future__ import print_function
 
 from sage.libs.singular.function import lib, singular_function
 from sage.misc.misc import repr_lincomb

src/sage/algebras/quatalg/quaternion_algebra_cython.pyx

@@ -20,7 +20,6 @@ AUTHORS:
 # (at your option) any later version.
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import absolute_import
 
 from sage.rings.integer_ring import ZZ
 from sage.rings.rational_field import QQ

src/sage/arith/multi_modular.pyx

@@ -11,7 +11,6 @@ Utility classes for multi-modular algorithms
 # (at your option) any later version.
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import absolute_import
 
 from cysignals.memory cimport check_allocarray, check_reallocarray, sig_free
 

src/sage/arith/srange.pyx

@@ -1,3 +1,4 @@
+# cython: language_level=2
 """
 Ranges and the ``[1,2,..,n]`` notation
 

src/sage/calculus/integration.pyx

@@ -25,7 +25,6 @@ AUTHORS:
 #  the License, or (at your option) any later version.
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import print_function, absolute_import
 
 from cysignals.signals cimport sig_on, sig_off
 from sage.rings.real_double import RDF

src/sage/calculus/interpolators.pyx

@@ -22,7 +22,6 @@ Development supported by NSF award No. 0702939.
 #
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import absolute_import
 
 import numpy as np
 cimport numpy as np

src/sage/calculus/ode.pyx

@@ -18,7 +18,6 @@ AUTHORS:
 # (at your option) any later version.
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import absolute_import
 
 from cysignals.memory cimport sig_malloc, sig_free
 from cysignals.signals cimport sig_on, sig_off

src/sage/calculus/riemann.pyx

@@ -24,7 +24,6 @@ Development supported by NSF award No. 0702939.
 #
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import print_function, absolute_import
 
 from cysignals.signals cimport sig_on, sig_off
 

src/sage/calculus/transforms/dwt.pyx

@@ -20,7 +20,6 @@ AUTHOR:
 # (at your option) any later version.
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import absolute_import
 
 import sage.plot.all
 

src/sage/calculus/transforms/fft.pyx

@@ -19,7 +19,6 @@ AUTHORS:
 # (at your option) any later version.
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
-from __future__ import absolute_import
 
 from cysignals.memory cimport sig_malloc, sig_free