Reintroduce compatibility functions for a few release;

Leaving time for Cython to clean that up.

Closes  #12068

IPython/utils/py3compat.py

@@ -185,3 +185,10 b' def u_format(s):'
 PY2 = not PY3
 PYPY = platform.python_implementation() == "PyPy"
 
+# Cython still rely on that as a Dec 28 2019
+# See https://github.com/cython/cython/pull/3291 and
+# https://github.com/ipython/ipython/issues/12068
+def no_code(x, encoding=None):
+        return x
+unicode_to_str = cast_bytes_py2 = no_code
+