EuroPython 2015, Stefan Behnel

See http://consulting.behnel.de/

In [1]:
%load_ext cython
In [2]:
import sys
import Cython
print("Python %d.%d.%d %s %s" % sys.version_info)
print("Cython %s" % Cython.__version__)

Python 3.5.0 beta 3
Cython 0.23.beta1

Functions and Coercion

In [3]:
%%cython

def pyfunc(x):
    return x + 1

def cyfunc(int x):
    return x + 1

cdef int cfunc(int x):
    return x + 1

cpdef cypyfunc(int x):
    y = cfunc(x + 1)
    return y * 2
In [4]:
pyfunc(2)
Out[4]:
3
In [5]:
cyfunc(2)
Out[5]:
3
In [6]:
cfunc(2)

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-6-aad7450ab81e> in <module>()
----> 1 cfunc(2)

NameError: name 'cfunc' is not defined
In [7]:
cypyfunc(2)
Out[7]:
8

Function "JIT compiling"

In [8]:
# NOTE: Python code!

import cython

@cython.compile
def calc(a, b):
    for x in range(a):
        b += x
    return b
In [9]:
calc(10, 20)
Out[9]:
65
In [10]:
type(calc)
Out[10]:
Cython.Build.Inline.RuntimeCompiledFunction

Calling C functions

In [11]:
%%cython -a
# libc math functions
from libc cimport math

print( math.sin(math.M_PI / 2) )

1.0
Out[11]:
Cython: _cython_magic_7b59fd28fa04df04fc472da95cd2e5e6.pyx

Generated by Cython 0.23.beta1

Yellow lines hint at Python interaction.
Click on a line that starts with a "+" to see the C code that Cython generated for it. 

 1: # libc math functions
 2: from libc cimport math
 3: 
+4: print( math.sin(math.M_PI / 2) )
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  __Pyx_DECREF(__pyx_t_1); __pyx_t_1 = 0;
In [12]:
%%cython
# dynamic C memory allocation
from libc.stdlib cimport malloc, free

cdef int* cmem = <int*>malloc(22 * sizeof(int))
if not cmem:
    raise MemoryError()
free(cmem)
In [13]:
%%cython
# dynamic CPython heap memory allocation
from cpython.mem cimport PyMem_Malloc, PyMem_Free

cdef int* pymem = <int*>PyMem_Malloc(22 * sizeof(int))
if not pymem:
    raise MemoryError()
    
try:
    pymem[:] = [1,2,3]
    print( pymem[0] + pymem[2] )
finally:
    PyMem_Free(pymem)

4

Auto-wrapping C functions to Python

In [14]:
%%cython -a
from libc cimport math, stdlib
py_sin = math.sin
py_atoi = stdlib.atoi
Out[14]:
Cython: _cython_magic_ab2e08202c97f4fb1f1c8944ff80d90b.pyx

Generated by Cython 0.23.beta1

Yellow lines hint at Python interaction.
Click on a line that starts with a "+" to see the C code that Cython generated for it. 

+1: from libc cimport math, stdlib
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+2: py_sin = math.sin
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+3: py_atoi = stdlib.atoi
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In [15]:
py_sin(1/2)
Out[15]:
0.479425538604203
In [16]:
py_atoi(b'123')
Out[16]:
123

External libraries

In [17]:
%%cython
# distutils: include_dirs=/usr/include/luajit-2.0
# distutils: libraries=luajit-5.1

## distutils: include_dirs=/usr/include/lua5.1
## distutils: libraries=lua5.1

cdef extern from "lua.h":
    ctypedef struct lua_State
    lua_State *luaL_newstate ()
    void lua_close (lua_State *L)
    int luaL_loadbuffer (lua_State *L, char *buff, size_t sz, char *name)
    void lua_settop (lua_State *L, int idx)
    int lua_gettop (lua_State *L)
    int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc)
    int lua_type (lua_State *L, int idx)
    float lua_tonumber (lua_State *L, int idx)
    enum:
        LUA_TNUMBER
        LUA_MULTRET


def run_lua(code):
    cdef int result_status
    cdef float result

    if isinstance(code, unicode):
        code = code.encode('utf8')
    elif not isinstance(code, bytes):
        raise ValueError("code must be a string")

    # init Lua runtime
    L = luaL_newstate()
    if not L:
        raise MemoryError()

    try:
        # compile Lua code
        if luaL_loadbuffer(L, code, len(code), '<python>'):
            raise SyntaxError()

        # execute code
        if lua_pcall(L, 0, LUA_MULTRET, 0):
            raise RuntimeError()

        # convert return value (Lua number == float)
        assert lua_type(L, 1) == LUA_TNUMBER, "not a numeric return value"
        return lua_tonumber(L, 1)
    finally:
        lua_settop(L, 0)
        lua_close(L)
In [18]:
code = '''
function fib(i)
    if i > 2 then
        return fib(i-1) + fib(i-2)
    else
        return 1
    end
end
'''

run_lua(code + "return fib(10)")
Out[18]:
55.0
In [19]:
%%timeit bench = code + "return fib(24)"

run_lua(bench)

100 loops, best of 3: 2.15 ms per loop
In [20]:
# distutils: include_dirs=/usr/include/luajit-2.0
# distutils: libraries=luajit-5.1

C arrays

In [21]:
%%cython -a
def carrays():
    cdef int[10] a, b
    a[:5] = [1,2,3,4,5]
    b = a
    b[5:] = [6,7,8,9,10]

    for i in b[:3]:
        print(i+1)

    return b
Out[21]:
Cython: _cython_magic_0a0700be7e736bc6c3dc54429e7b8a95.pyx

Generated by Cython 0.23.beta1

Yellow lines hint at Python interaction.
Click on a line that starts with a "+" to see the C code that Cython generated for it. 

+01: def carrays():
/* Python wrapper */
static PyObject *__pyx_pw_46_cython_magic_0a0700be7e736bc6c3dc54429e7b8a95_1carrays(PyObject *__pyx_self, CYTHON_UNUSED PyObject *unused); /*proto*/
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 02:     cdef int[10] a, b
+03:     a[:5] = [1,2,3,4,5]
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+04:     b = a
  memcpy(&(__pyx_v_b[0]), __pyx_v_a, sizeof(__pyx_v_b[0]) * (10));

+05:     b[5:] = [6,7,8,9,10]
  __pyx_t_2[0] = 6;
  __pyx_t_2[1] = 7;
  __pyx_t_2[2] = 8;
  __pyx_t_2[3] = 9;
  __pyx_t_2[4] = 10;
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 06: 
+07:     for i in b[:3]:
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+08:         print(i+1)
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 09: 
+10:     return b
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In [22]:
carrays()

2
3
4
Out[22]:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

C tuples

In [23]:
%%cython -a

def ctuples():
    cdef int a = 42
    cdef double b = a / 5.0

    cdef (int, double) t = (a, b)
    print(t[0])
    print(t[1])
    print(t)

    return t
Out[23]:
Cython: _cython_magic_28b17313f2e630a40c1e37e0dbcc1e7e.pyx

Generated by Cython 0.23.beta1

Yellow lines hint at Python interaction.
Click on a line that starts with a "+" to see the C code that Cython generated for it. 

 01: 
+02: def ctuples():
/* Python wrapper */
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 10: 
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In [24]:
ctuples()

42
8.4
(42, 8.4)
Out[24]:
(42, 8.4)

C++

In [25]:
%%cython -a
# distutils: language=c++


from libcpp.vector cimport vector

def func():
    cdef vector[int] v
    v.push_back(10)
    return v
Out[25]:
Cython: _cython_magic_a1e5605f1fdd147ec2c410b3c5d592f5.pyx

Generated by Cython 0.23.beta1

Yellow lines hint at Python interaction.
Click on a line that starts with a "+" to see the C code that Cython generated for it. 

+1: # distutils: language=c++
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 2: 
 3: 
 4: from libcpp.vector cimport vector
 5: 
+6: def func():
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In [27]:
%%cython -a
# distutils: language=c++

from libcpp.vector cimport vector

cdef class Integers:
    cdef vector[int] _values

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In [28]:
x = Integers()
x.add(2)
x.add(3)
x
Out[28]:
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