Compiler directive language_level is ignored if no Python statement is written before it.

[rsaim]

$ cat temp.pyx
# cython: language_level=3
print("abc", "def", sep=" ,") # invalid in python 2

Compiling:

$ cythonize -i world_dep.pyx
Error compiling Cython file:
------------------------------------------------------------
...
# cython: language_level=3

print("abc", "def", sep=" ,")                      ^
------------------------------------------------------------
temp.pyx:4:23: Expected ')', found '='

So lanugage_level directive is not getting respected. Thus, cythonize ends up using Python 2 semantics and the error is thrown as the print statement above is invalid in Python 2.

However, including any Python statement before the print statement makes this work:

 $ cat temp.pyx
 # cython: language_level=3
 import os
 print("abc", "def", sep=" ,")
Compiling and executing:

$ cythonize -i temp.pyx; python -c "import temp"
abc, def

[pdebuyl]

I confirm with cython 0.26.1 on Python 2.7 and 3.6 (debian, x86_64) and cython 0.28.2 (from pip).

As a test, if indeed the directive "skips" the first line, I checked the following:

# cython: language_level=3
print 1
print("abc", "def", sep=" ,")

And it compiles and runs properly. cythonize will also build the snippet above when given the -3 option but cython will not (with option -3).