Cython is a programming language that allows writing Python code that is compiled to C/C++ extensions. This results in code that runs as fast as compiled C while maintaining the flexibility of Python. Cython code can be directly interfaced with C libraries for improved performance. The source code is annotated with type declarations for variables and functions to enable static type checking and optimization. This often results in performance gains of 100x or more compared to regular Python code.

1. Cython
Close to the metal Python
Kyiv.py #10
Taras Lyapun

2. Python is a wonderful language that
allows us to solve problems quickly and
elegantly, but...

3. ...but nothing ideal in this world. As a
interpreted, dynamical language without
static typization, Python is slow.

4. How many times have you heard or said,
"We can always rewrite bottlenecks on
C"?

5. How can we do this?
- By hand using Python C API
- SWIG
- Boost.Python
- ctypes
- SIP, Py++, f2py, PyD, Interrogate, Robin, ...
- Cython

6. Cython
- Programming language based on Python
- The source code gets translated into
optimized C/C++ code and compiled as Python
extension modules
- Originally based on the well-known Pyrex
- This code is executed within the CPython
runtime environment, but at the speed of
compiled C and with the ability to call directly
into C libraries.

7. Install
pip install cython

8. Building with a distutils
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
ext_modules = [Extension("hello", ["hello.pyx"])]
setup(
name = 'Hello world app',
cmdclass = {'build_ext': build_ext},
ext_modules = ext_modules
)
python setup.py build_ext --inplace

9. Building with pyximport
import pyximport
pyximport.install()

10. Building manually
cython path/to/your.pyx
gcc ...

11. Workflow
- Python code
- Profiling
- Unittests
- Cython code

12. Original

13. mv util.py util.pyx
x2 performance

14. cython -a util.pyx

15. Just add static typization
ncalls tottime percall cumtime percall filename:lineno(function)
8 0.010 0.001 0.010 0.001 {qrcode.util.lost_point}
x16 performance.
Easy achieve 100-1000x!

16. cython -a util.pyx

17. Overview
- Almost like Python (with few exceptions)
- top-level classes and functions
- loops, with, try-except/finally...
- lambda
- generators
- import
- Py3 support

18. Type declaration
- cdef - for static typization
cdef double dx, s
- cdef - as a C function
cdef double f(double x):
return sin(x**2)
- cdef class - extensions
cdef class MyType:
cdef int field
- cpdef - C function + Python wrapper

19. Classes
cdef class MyClass(SomeClass):
- "builtin" extension type
- single inheritance, only from other extension
types
- fixed, typed fields
- C-only access by default, or readonly/public
- Python + C methods

20. Pure python mode
@cython.ccall
@cython.returns(cython.double)
@cython.locals(x=cython.double, y=cython.
double)
def float_mult(x, y):
return x * y

21. Pure python mode
# test.py
def float_mult(x, y):
return x * y
# test.pxd
cpdef double float_mult(double x, double y)
(but no access to C functions)

22. Exceptions
cdef double f(double x) except -1:
cdef double f(double x) except? -1:
cdef int spam() except *:
cdef int spam() except +:

23. Exceptions
File "run.py", line 9, in <module>
"""
File "qrcode/main.py", line 7, in make
return qr.make_image()
File "qrcode/main.py", line 169, in make_image
self.make()
File "qrcode/main.py", line 53, in make
self.best_fit(start=self.version)
File "qrcode/main.py", line 108, in best_fit
self.error_correction, self.data_list)
File "util.pyx", line 401, in qrcode.util.create_data (qrcode/util.c:7844)
File "util.pyx", line 418, in qrcode.util.create_data (qrcode/util.c:7513)
qrcode.util.DataOverflowError: Code length overflow. Data size (916) > size
available (128)

24. Profiling
# cython: profile=True
@cython.profile(False)
cython -X profile=True ...

25. Also
- debugging with GDB
- Easy wrap C/C++ libraries
- Numpy, cmath, etc
- with nogil - release GIL
- cython.parallel - for native parallelism (OpenMP)
- and a lot of other cool hackers things

26. Thanks!
http://cython.org/