Python高级编程（二）

Advanced Python
Programming (Part II)
Happy Day #5
2011.10

Topics

• Performance Tuning
• Garbage Collection
• Extending Python

Python's Speed
Among Most Popular Languages

C C++ Java Lisp C# Pascal Python Ruby PHP Perl
data source (on Oct.17, 2011):
• http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html
• http://shootout.alioth.debian.org/u64q/which-programming-languages-are-fastest.php

7 Steps to Gain Speed
1) Find performance bottlenecks
2) Use better algorithms
3) Use faster tools
4) Write optimized code
5) Hire optimizers
6) Write your own extension modules
7) Parallelize the computation

Step 0
Is It Fast Enough Already?

Step 1
Find Performance Bottlenecks

Find Performance
Bottlenecks
• Profile, no guess
- profile
• a pure Python module
- cProfile
• written in C, new in Python 2.5
• same interface with profile, but lower overhead
- hotshot
• written in C, new in Python 2.2
• not maintained and might be removed

cProfile Usage
• cProfile.run('foo()')
• cProfile.run('foo()', 'profile.result')
• python -m cProfile -o profile.result myscript.py
• p = pstats.Stats('profile.result')
• p.sort_stats('cumulative').print_stats()
• sort by 'cumulative' to find what algorithms are taking time
• sort by 'time' to find what functions are taking time
• RunSnakeRun for GUI guys
• RTFM, please
• for IPython, type %prun?

Line Proﬁle
• line_proﬁle and kernprof
@profile
def slow_function():
...

$ kernprof.py -l -v script_to_profile.py
...
Line # Hits Time Per Hit % Time Line Contents
==============================================================
1 @profile
2 def slow_function():
3 1 3 3.0 0.2 s = 0
4 1001 934 0.9 48.6 for i in xrange(1000):
5 1000 984 1.0 51.2 s += i
6 1 1 1.0 0.1 return s

How To Know Which is
Better?
• timeit!
• python -m timeit -s "setup" "statement"
• e.g. which is faster, "d.has_key(k)" or "k in
d"?
$ python -m timeit -s "d=dict(zip(range(1000), range(1000)))"
"d.has_key(500)"
1000000 loops, best of 3: 0.223 usec per loop

$ python -m timeit -s "d=dict(zip(range(1000), range(1000)))"
"500 in d"
10000000 loops, best of 3: 0.115 usec per loop

Use Bettern Algorithms
• How to calculate sum([1, 2, ..., 100])?

s = 0
for i in range(101): 8.3usec
s += i

s = 0
s += i

s = sum(range(101)) 2.8usec

s = 0
s += i

s = sum(xrange(101)) 2.03usec

s = 0
s += i

s = sum(xrange(101)) 2.03usec
s = (1 + 100) * 100 / 2 0.109usec

Advanced Data Types
• membership testing:
• set & dict: O(1) vs. tuple & list: O(n)
• return iterator instead of a large list
• array, collections.deque, heapq, bisect

Examples
lst = []
for i in xrange(10000):
lst.insert(0, i)

lst = collections.deque()
for i in xrange(10000): 25317% faster
lst.appendleft(i)

sorted(lst, reverse=True)[:10]

heapq.nlargest(10, lst)
613% faster

Do Less Computation

• Pre-computation
• Lazy computation
• Cache
• Approximation Algorithms

Example
def fib(n):
if n <= 1:
return 1 ﬁb(25): 59.8ms
return fib(n-2) + fib(n-1)

Example
def cache(func):
c = {}
def _(n):
r = c.get(n) ﬁb(25): 59.8ms
if r is None:
r = c[n] = func(n)
return r
return _ with @cache:
@cache ﬁb(25): 0.524us
def fib(n):
if n <= 1:
return 1 112000 times faster!
return fib(n-2) + fib(n-1)

Use Faster Tools
• use iterator form
• range() -> xrange()
• map() -> itertools.imap()
• list comprehension -> generator expression
• dict.items() -> dict.iteritems()
• for i in range(len(seq)): ->
• for item in seq:
• for i, item in enumerate(seq):

Use Faster Tools
• SAX is faster and memory efficient than DOM
• use C version of modules
• profile -> cProfile
• StringIO -> cStringIO
• pickle -> cPickle
• elementTree -> cElementTree / lxml
• select has lower overhead than poll (and epoll at low
number of connections)
• numpy is essential for high volume numeric work

numpy Example
from itertools import izip
a=range(1000)
b=range(1000)
c = [ai+bi for ai, bi in izip(a, b)]

import numpy
a=numpy.arange(1000)
b=numpy.arange(1000)
c = a + b

Write Optimized Code

• Less temporary objects
• e.g. accumulator vs. sum
• however, string concatenation has been
optimized after Python 2.5

• use key= instead of cmp= when sorting
lst = open('/Users/hongqn/projects/shire/luzong/
group.py').read().split()

lst.sort(cmp=lambda x, y: cmp(x.lower(), y.lower()))

lst.sort(key=str.lower) 377% faster

• local variables are faster than global
variables
def f():
r = abs(i)

def f():
_abs = abs
r = _abs(i)
28% faster

• you can eliminate dots, too

• inline function inside time-critical loops
def f(x):
return x + 1
r = f(i)

r = i + 1 187% faster

• do not import modules in loops
import string
r = string.lower('Python')

import string
r = string.lower('Python')
178% faster

• list comprehensions are faster than for-
loops
lst = []
lst.append(i)

lst = [i for i in xrange(10000)] 213% faster

• use "while 1" for time-critical loops
(readability lost!)
a = 0
while True:
a += 1
if a > 10000:
break

a = 0
while 1:
a += 1
if a > 10000: 78% faster
break

• "not not x" is faster than "bool(x)" (not
recommended!)
bool([])

not not [] 196% faster

Hire Optimizers

• sys.setcheckinterval()
• Python checks for thread switch and
signal handling periodly (default 100
python virtual instructions)
• set it to a larger value for better
performance in cost of responsiveness

Hire Optimizers

• gc.disable()
• disable automatic garbage collection
• gc.set_threshold()
• collect less frequently

Hire Optimizers
• Psyco
• JIT for 32bit only. <=Python 2.6
• PyPy
• Alternative implementation of Python
• Shed Skin
• Python-to-C++ compiler
• numexpr
• numpy expression evaluator

Step 6
Write Your Own Extension Modules

Write Your Own
Extension Modules
• Python/C API
• Ofﬁcial API
• ctypes
• Call dynamic link library in Python
• SWIG
• Automatically generate interface code
• Pyrex / Cython
• write extension using Python-like language
• Boost.Python
• C++ API
• Weave
• Inline C code

Write Your Own
Extension Modules

• C-level Optimization

Step 7
Parallelize the Computation

Over CPUs
• multi-threading
• threading (be careful with GIL!)
• multi-processing
• fork
• subprocess
• multiprocessing
• async
• asyncore
• twisted
• greenlet/gevent
• PyOpenCL / PyCUDA

multiprocessing
Example
sum(xrange(1, 10000001)) 172ms

from multiprocessing import Pool
pool = Pool()
sum(pool.map(sum, (xrange(i, i+1000000)
for i in xrange(1, 10000000, 1000000))))

104ms on dual-core
49ms on 8-core

Over Cluster
• XML-RPC / Json-RPC / Thrift / Protocol
Buffer
• Pyro
• Parallel Python
• dumbo on Hadoop
• dpark

Gold Rule

Premature optimization is the root of all evil.
-- Donald Knuth

What Is Garbage

• An object which will not be used in any
future
• i.e. no other object refers to it

Why Collecting
Garbage?

• re-sell it (recycle)
• make programs simpler

Garbage Collection in
Everywhere

• by lilinghui, Sep.20, 2011
• http://svn.douban.com/projects/shire/wiki/
HallOfFire/Platform

Basic Garbage
Collection Algorithms
• Reference couting
• Mark-and-sweep
• Mark-and-compact
• Copy

Garbage Collection in
CPython

• Reference couting
• Mark-and-sweep

Reference Counting
def f():
a = A()
a.b = B()
a.b.c = C()
a.c = b.c

Reference Counting
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.c = b.c
1 1

c
2

Reference Counting
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.c = b.c
1 1
del a.c

c
2

Reference Counting
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.c = b.c
1 1
del a.c

c
1

Reference Counting
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.c = b.c
1 1
del a.c
del a.b
c
1

Reference Counting
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.c = b.c
1 0
del a.c
del a.b
c
1

Reference Counting
def f(): frame
a = A()
a.b = B()
a.b.c = C() a
a.c = b.c
1
del a.c
del a.b
c
0

Reference Counting
def f(): frame
a = A()
a.b = B()
a.b.c = C() a
a.c = b.c
1
del a.c
del a.b

Reference Counting
def f():
a = A()
a.b = B()
a.b.c = C() a
a.c = b.c
0
del a.c
del a.b

Reference Counting
def f():
a = A()
a.b = B()
a.b.c = C()
a.c = b.c
del a.c
del a.b

Pros & Cons of
Reference Counting
• Pros
• collect early
• predictable run-time behavior
• Cons
• slow
• circle reference

Circle Reference
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.b.c.b = a.b
1 2

c
1

Circle Reference
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.b.c.b = a.b
1 2
del a.b

c
1

Circle Reference
def f(): frame
a = A()
a.b = B()
a.b.c = C() a b
a.b.c.b = a.b
1 1
del a.b

c
1

Circle Reference
def f():
a = A()
a.b = B()
a.b.c = C() b
a.b.c.b = a.b
1
del a.b

c
1

Weak Reference
a reference not strong enough to keep an object alive

>>> import weakref import weakref
>>> class Object:
... pass _id2obj_dict = weakref.WeakValueDictionary()
...
>>> o = Object() def remember(obj):
>>> r = weakref.ref(o) oid = id(obj)
>>> o2 = r() _id2obj_dict[oid] = obj
>>> o is o2 return oid
True
>>> del o, o2 def id2obj(oid):
>>> print r() return _id2obj_dict[oid]
None

Mark-and-Sweep
frame
1. Mark root objects
and all their referents
reachable a b
2. Sweep unreachable 1 1
objects
c
1

Generations
• generations and thresholds
• generation 0 (youngest): 700
• generation 1 (middle):10
• generation 2 (oldest): 10
• and long_lived_pending /
long_lived_total > 25% (Python 2.7+)

Python's Optimization

• Track only container objects
• Use referent count to ﬁnd root objects

__del__

• circle referenced objects with __del__()
methods will be put in gc.garbage
• do not use __del__

GC Module
• gc.enable() / gc.disable()
• gc.collect()
• gc.get_threshold() / gc.set_threshold()
• gc.set_debug()
• gc.get_referers() / gc.get_referents()
• gc.get_objects()

#include <Python.h>

static PyObject *SpamError;

static PyObject *
spam_system(PyObject *self, PyObject *args)
{
const char *command;
int sts;

if (!PyArg_ParseTuple(args, "s", &command))
return NULL;
sts = system(command);
if (sts < 0) {
PyErr_SetString(SpamError, "System command failed");
return NULL;
}
return PyLong_FromLong(sts);
}

static PyMethodDef SpamMethods[] = {
{"system", spam_system, METH_VARARGS,
"Execute a shell command."},
{NULL, NULL, 0, NULL} /* Sentinel */
};

PyMODINIT_FUNC
initspam(void)
{
PyObject *m;

m = Py_InitModule("spam", SpamMethods);
if (m == NULL)
return;

SpamError = PyErr_NewException("spam.error", NULL, NULL);
Py_INCREF(SpamError);
PyModule_AddObject(m, "error", SpamError);
}

Building with
setuptools
from setuptools import setup, Extension

module1 = Extension('spam',
sources = ['spam.c'])

setup (name = 'PackageName',
version = '1.0',
description = 'This is a demo package',
ext_modules = [module1])

python setup.py install
python setup.py build_ext --inplace

Parse and Build Values
• int PyArg_ParseTuple(PyObject *args,
const char *format, ...)

• int PyArg_ParseTupleAndKeywords(PyObject
*args, PyObject *kw, const char *format,
char *keywords[], ...)

• int PyArg_BuildValue(const char
*format, ...)

Manage Reference
Counting
• Py_INCREF(PyObject *o) /
Py_XINCREF(PyObject *o)
• Py_DECREF(PyObject *o) /
Py_XINCREF(PyObject *o) /
Py_CLEAR(PyObject *o)
• New/Borrowed/Stealing references

Exception Handling
• errno-like mechanism
• PyErr_SetString() / PyErr_SetObject() to
set error
• PyErr_Occurred() to check error
• Most functions return an error indicator,
e.g. NULL, -1

Global Interpreter Lock
• Release GIL before running blocking C code
Py_BEGIN_ALLOW_THREADS
...Do some blocking I/O operation...
Py_END_ALLOW_THREADS

• Reacquire GIL before calling into Python functions
PyGILState_STATE gstate;
gstate = PyGILState_Ensure();

/* Perform Python actions here. */
result = CallSomeFunction();
/* evaluate result */

/* Release the thread. No Python API allowed beyond this point. */
PyGILState_Release(gstate);

Python Style Code
from libc.stdlib cimport system as c_system

class error(Exception):
pass

def system(char* cmd):
cdef int retval = c_system(cmd)
if retval < 0:
raise error("System command failed")
return retval

setup.py
from setuptools import setup, Extension
from Cython.Distutils import build_ext

extmod = Extension("spam", sources=['spam.pyx'])

setup(
name="Spam",
cmdclass = {'build_ext': build_ext},
ext_modules = [extmod])

#include <Python.h>
#include "structmember.h"
static PyGetSetDef Noddy_getseters[] = {

Extension Types
typedef struct { {"first",
PyObject_HEAD (getter)Noddy_getfirst, (setter)Noddy_setfirst,
PyObject *first; "first name",
PyObject *last; NULL},
int number; {"last",
} Noddy; (getter)Noddy_getlast, (setter)Noddy_setlast,
"last name",
static void NULL},
Noddy_dealloc(Noddy* self) {NULL} /* Sentinel */
{ };
Py_XDECREF(self->first);
Py_XDECREF(self->last); static PyObject *
self->ob_type->tp_free((PyObject*)self); Noddy_name(Noddy* self)
} {
static PyObject *format = NULL;
static PyObject * PyObject *args, *result;
Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{ if (format == NULL) {
Noddy *self; format = PyString_FromString("%s %s");
if (format == NULL)
self = (Noddy *)type->tp_alloc(type, 0); return NULL;
if (self != NULL) { }
self->first = PyString_FromString("");
if (self->first == NULL) args = Py_BuildValue("OO", self->first, self->last);
{ if (args == NULL)
Py_DECREF(self); return NULL;
return NULL;
} result = PyString_Format(format, args);
Py_DECREF(args);
self->last = PyString_FromString("");
if (self->last == NULL) return result;
{ }
Py_DECREF(self);
return NULL; static PyMethodDef Noddy_methods[] = {
} {"name", (PyCFunction)Noddy_name, METH_NOARGS,
"Return the name, combining the first and last name"
self->number = 0; },
} {NULL} /* Sentinel */
};
return (PyObject *)self;
} static PyTypeObject NoddyType = {
PyObject_HEAD_INIT(NULL)
static int 0, /*ob_size*/
Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) "noddy.Noddy", /*tp_name*/
{ sizeof(Noddy), /*tp_basicsize*/
PyObject *first=NULL, *last=NULL, *tmp; 0, /*tp_itemsize*/
(destructor)Noddy_dealloc, /*tp_dealloc*/
static char *kwlist[] = {"first", "last", "number", NULL}; 0, /*tp_print*/
0, /*tp_getattr*/
if (! PyArg_ParseTupleAndKeywords(args, kwds, "|SSi", kwlist, 0, /*tp_setattr*/
&first, &last, 0, /*tp_compare*/
&self->number)) 0, /*tp_repr*/
return -1; 0, /*tp_as_number*/
0, /*tp_as_sequence*/
if (first) { 0, /*tp_as_mapping*/
tmp = self->first; 0, /*tp_hash */
Py_INCREF(first); 0, /*tp_call*/
self->first = first; 0, /*tp_str*/
Py_DECREF(tmp); 0, /*tp_getattro*/
} 0, /*tp_setattro*/
0, /*tp_as_buffer*/
if (last) { Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
tmp = self->last; "Noddy objects", /* tp_doc */
Py_INCREF(last); 0,! ! /* tp_traverse */
self->last = last; 0,! ! /* tp_clear */
Py_DECREF(tmp); 0,! ! /* tp_richcompare */
} 0,! ! /* tp_weaklistoffset */
0,! ! /* tp_iter */
return 0; 0,! ! /* tp_iternext */
} Noddy_methods, /* tp_methods */
Noddy_members, /* tp_members */
static PyMemberDef Noddy_members[] = { Noddy_getseters, /* tp_getset */
{"number", T_INT, offsetof(Noddy, number), 0, 0, /* tp_base */
"noddy number"}, 0, /* tp_dict */
{NULL} /* Sentinel */ 0, /* tp_descr_get */
}; 0, /* tp_descr_set */
0, /* tp_dictoffset */
static PyObject * (initproc)Noddy_init, /* tp_init */
Noddy_getfirst(Noddy *self, void *closure) 0, /* tp_alloc */
{ Noddy_new, /* tp_new */
Py_INCREF(self->first); };
return self->first;
} static PyMethodDef module_methods[] = {
{NULL} /* Sentinel */
static int };
Noddy_setfirst(Noddy *self, PyObject *value, void *closure)
{ #ifndef PyMODINIT_FUNC! /* declarations for DLL import/export */
if (value == NULL) { #define PyMODINIT_FUNC void
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute"); #endif
return -1; PyMODINIT_FUNC
} initnoddy3(void)
{
if (! PyString_Check(value)) { PyObject* m;
PyErr_SetString(PyExc_TypeError,
"The first attribute value must be a string"); if (PyType_Ready(&NoddyType) < 0)
return -1; return;
}
m = Py_InitModule3("noddy3", module_methods,
Py_DECREF(self->first); "Example module that creates an extension type.");
Py_INCREF(value);
self->first = value; if (m == NULL)
return;
return 0;
} Py_INCREF(&NoddyType);
PyModule_AddObject(m, "Noddy", (PyObject *)&NoddyType);
static PyObject * }
Noddy_getlast(Noddy *self, void *closure)
{
Py_INCREF(self->last);
return self->last;
}

static int
Noddy_setlast(Noddy *self, PyObject *value, void *closure)
{
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
return -1;
}

if (! PyString_Check(value)) {
"The last attribute value must be a string");
return -1;
}

Py_DECREF(self->last);
Py_INCREF(value);
self->last = value;

return 0;
}

#include <Python.h>
#include "structmember.h"
static PyGetSetDef Noddy_getseters[] = {

Extension Types
typedef struct { {"first",
PyObject_HEAD (getter)Noddy_getfirst, (setter)Noddy_setfirst,
PyObject *first; "first name",
PyObject *last; NULL},
int number; {"last",
} Noddy; (getter)Noddy_getlast, (setter)Noddy_setlast,
"last name",
static void NULL},
Noddy_dealloc(Noddy* self) {NULL} /* Sentinel */
{ };
Py_XDECREF(self->first);
Py_XDECREF(self->last); static PyObject *
self->ob_type->tp_free((PyObject*)self); Noddy_name(Noddy* self)
} {
static PyObject *format = NULL;
static PyObject * PyObject *args, *result;
Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{ if (format == NULL) {
Noddy *self; format = PyString_FromString("%s %s");
if (format == NULL)
self = (Noddy *)type->tp_alloc(type, 0); return NULL;
if (self != NULL) { }
self->first = PyString_FromString("");
if (self->first == NULL) args = Py_BuildValue("OO", self->first, self->last);
{ if (args == NULL)
Py_DECREF(self); return NULL;
return NULL;
} result = PyString_Format(format, args);
Py_DECREF(args);
self->last = PyString_FromString("");
if (self->last == NULL) return result;
{
Py_DECREF(self);
}
cdef class Noddy:
return NULL; static PyMethodDef Noddy_methods[] = {
} {"name", (PyCFunction)Noddy_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
"""Noddy objects"""
self->number = 0;
} {NULL} /* Sentinel */
};
return (PyObject *)self;
}

static int
static PyTypeObject NoddyType = {
PyObject_HEAD_INIT(NULL)
0, /*ob_size*/
cdef object first, last
"noddy.Noddy", /*tp_name*/
Noddy_init(Noddy *self, PyObject *args, PyObject *kwds)
{
PyObject *first=NULL, *last=NULL, *tmp;
sizeof(Noddy),
0,
/*tp_basicsize*/
/*tp_itemsize*/
cdef public int number
(destructor)Noddy_dealloc, /*tp_dealloc*/
static char *kwlist[] = {"first", "last", "number", NULL}; 0, /*tp_print*/
0, /*tp_getattr*/
if (! PyArg_ParseTupleAndKeywords(args, kwds, "|SSi", kwlist, 0, /*tp_setattr*/
&first, &last,
&self->number))
0,
0,
0,
/*tp_compare*/
/*tp_repr*/
/*tp_as_number*/
def __cinit__(self, str first="", str last="", int number=0):
return -1;

if (first) {
0,
0,
0,
/*tp_as_sequence*/
/*tp_as_mapping*/
/*tp_hash */
self.first = first
tmp = self->first;
Py_INCREF(first);
self->first = first;
Py_DECREF(tmp);
0,
0,
0,
/*tp_call*/
/*tp_str*/
/*tp_getattro*/
self.last = last
0, /*tp_setattro*/
}

if (last) {
0, /*tp_as_buffer*/
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
self.number = number
tmp = self->last; "Noddy objects", /* tp_doc */
Py_INCREF(last); 0,! ! /* tp_traverse */
self->last = last; 0,! ! /* tp_clear */
Py_DECREF(tmp); 0,! ! /* tp_richcompare */
} 0,!
0,!
0,!
!
!
!
/* tp_weaklistoffset */
/* tp_iter */
/* tp_iternext */
property first:
return 0;
} Noddy_methods,
Noddy_members,
Noddy_getseters,
/* tp_methods */
/* tp_members */
/* tp_getset */
"""first name"""
static PyMemberDef Noddy_members[] = {
{"number", T_INT, offsetof(Noddy, number), 0,
"noddy number"},
{NULL} /* Sentinel */
0,
0,
0,
/* tp_base */
/* tp_dict */
/* tp_descr_get */
def __get__(self):
0, /* tp_descr_set */
};

static PyObject *
0,
(initproc)Noddy_init,
/* tp_dictoffset */
/* tp_init */
return self.first
Noddy_getfirst(Noddy *self, void *closure) 0, /* tp_alloc */
{
Py_INCREF(self->first); };
Noddy_new, /* tp_new */
def __set__(self, str value):
return self->first;
} static PyMethodDef module_methods[] = {

};
{NULL} /* Sentinel */ self.first = value
static int
Noddy_setfirst(Noddy *self, PyObject *value, void *closure)
{ #ifndef PyMODINIT_FUNC! /* declarations for DLL import/export */
if (value == NULL) { #define PyMODINIT_FUNC void

}
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
#endif
PyMODINIT_FUNC
initnoddy3(void)
property last:
{
PyObject* m; """last name"""
"The first attribute value must be a string"); if (PyType_Ready(&NoddyType) < 0)

}
return -1; return;
def __get__(self):
m = Py_InitModule3("noddy3", module_methods,
Py_DECREF(self->first);
Py_INCREF(value);
if (m == NULL)
"Example module that creates an extension type.");
return self.last
self->first = value;

return 0;
return;

Py_INCREF(&NoddyType);
def __set__(self, str value):
}

static PyObject *
Noddy_getlast(Noddy *self, void *closure)
}
PyModule_AddObject(m, "Noddy", (PyObject *)&NoddyType);
self.last = value
{
Py_INCREF(self->last);
return self->last;
}

static int
def name(self):
Noddy_setlast(Noddy *self, PyObject *value, void *closure)
{
if (value == NULL) {
"""Return the name, combining the first and last name"""
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");

}
return -1;
return "%s %s" % (self.first, self.last)
"The last attribute value must be a string");
return -1;
}

Py_DECREF(self->last);
Py_INCREF(value);
self->last = value;

return 0;
}

GIL
with nogil:
...

cdef void my_callback(void *data) with gil:
...

cdef void my_gil_free_func(int spam) nogil:
...

Call C Function in
Python
from ctypes import cdll
libc = cdll.LoadLibrary('libc.dylib')

class error(Exception):
pass

def system(cmd):
retval = libc.system(cmd)
if retval < 0:
raise error("System command failed.")
return retval

GIL

• ctypes.cdll: Release GIL
• ctypes.pydll: With GIL

Python高级编程（二）

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Python高级编程（二） (20)

Recently uploaded (20)

Python高级编程（二）