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move ctypes order
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@crazyguitar
crazyguitar committed Oct 5, 2018
1 parent 8c5b430 commit 8b9c2d0
Showing 1 changed file with 142 additions and 142 deletions.
284 changes: 142 additions & 142 deletions docs/notes/python-capi.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -6,148 +6,6 @@ Python C API cheatsheet
:backlinks: none


Performance of ctypes
----------------------

.. code-block:: c
// Compile (Mac)
// -------------
//
// $ clang -Wall -Werror -shared -fPIC -o libfib.dylib fib.c
//
unsigned int fib(unsigned int n)
{
if ( n < 2) {
return n;
}
return fib(n-1) + fib(n-2);
}
Compare the performance with pure Python

.. code-block:: python
>>> from time import time
>>> from ctypes import CDLL
>>> def fib(n):
... if n < 2: return n
... return fib(n - 1) + fib(n - 2)
...
>>> cfib = CDLL("./libfib.dylib").fib
>>> s = time(); _ = fib(35); e = time(); e - s
4.918856859207153
>>> s = time(); _ = cfib(35); e = time(); e - s
0.07283687591552734
Error handling when using ctypes
---------------------------------

.. code-block:: python
from __future__ import print_function
import os
from ctypes import *
from sys import platform, maxsize
is_64bits = maxsize > 2 ** 32
if is_64bits and platform == "darwin":
libc = CDLL("libc.dylib", use_errno=True)
else:
raise RuntimeError("Not support platform: {}".format(platform))
stat = libc.stat
class Stat(Structure):
"""
From /usr/include/sys/stat.h
struct stat {
dev_t st_dev;
ino_t st_ino;
mode_t st_mode;
nlink_t st_nlink;
uid_t st_uid;
gid_t st_gid;
dev_t st_rdev;
#ifndef _POSIX_SOURCE
struct timespec st_atimespec;
struct timespec st_mtimespec;
struct timespec st_ctimespec;
#else
time_t st_atime;
long st_atimensec;
time_t st_mtime;
long st_mtimensec;
time_t st_ctime;
long st_ctimensec;
#endif
off_t st_size;
int64_t st_blocks;
u_int32_t st_blksize;
u_int32_t st_flags;
u_int32_t st_gen;
int32_t st_lspare;
int64_t st_qspare[2];
};
"""
_fields_ = [
("st_dev", c_ulong),
("st_ino", c_ulong),
("st_mode", c_ushort),
("st_nlink", c_uint),
("st_uid", c_uint),
("st_gid", c_uint),
("st_rdev", c_ulong),
("st_atime", c_longlong),
("st_atimendesc", c_long),
("st_mtime", c_longlong),
("st_mtimendesc", c_long),
("st_ctime", c_longlong),
("st_ctimendesc", c_long),
("st_size", c_ulonglong),
("st_blocks", c_int64),
("st_blksize", c_uint32),
("st_flags", c_uint32),
("st_gen", c_uint32),
("st_lspare", c_int32),
("st_qspare", POINTER(c_int64) * 2),
]
# stat success
path = create_string_buffer(b"/etc/passwd")
st = Stat()
ret = stat(path, byref(st))
assert ret == 0
# if stat fail, check errno
path = create_string_buffer(b"&%$#@!")
st = Stat()
ret = stat(path, byref(st))
if ret != 0:
errno = get_errno() # get errno
errmsg = "stat({}) failed. {}".format(path.raw, os.strerror(errno))
raise OSError(errno, errmsg)
output:

.. code-block:: console
$ python err_handling.py # python2
Traceback (most recent call last):
File "err_handling.py", line 85, in <module>
raise OSError(errno_, errmsg)
OSError: [Errno 2] stat(&%$#@!) failed. No such file or directory
$ python3 err_handling.py # python3
Traceback (most recent call last):
File "err_handling.py", line 85, in <module>
raise OSError(errno_, errmsg)
FileNotFoundError: [Errno 2] stat(b'&%$#@!\x00') failed. No such file or directory
Simple setup.py for c extension
----------------------------------

Expand Down Expand Up @@ -551,3 +409,145 @@ Compare the performance with pure Python
4.953313112258911
>>> s = time(); _ = foo.fib(35); e = time(); e - s
0.04628586769104004
Performance of ctypes
----------------------

.. code-block:: c
// Compile (Mac)
// -------------
//
// $ clang -Wall -Werror -shared -fPIC -o libfib.dylib fib.c
//
unsigned int fib(unsigned int n)
{
if ( n < 2) {
return n;
}
return fib(n-1) + fib(n-2);
}
Compare the performance with pure Python

.. code-block:: python
>>> from time import time
>>> from ctypes import CDLL
>>> def fib(n):
... if n < 2: return n
... return fib(n - 1) + fib(n - 2)
...
>>> cfib = CDLL("./libfib.dylib").fib
>>> s = time(); _ = fib(35); e = time(); e - s
4.918856859207153
>>> s = time(); _ = cfib(35); e = time(); e - s
0.07283687591552734
Error handling when using ctypes
---------------------------------

.. code-block:: python
from __future__ import print_function
import os
from ctypes import *
from sys import platform, maxsize
is_64bits = maxsize > 2 ** 32
if is_64bits and platform == "darwin":
libc = CDLL("libc.dylib", use_errno=True)
else:
raise RuntimeError("Not support platform: {}".format(platform))
stat = libc.stat
class Stat(Structure):
"""
From /usr/include/sys/stat.h
struct stat {
dev_t st_dev;
ino_t st_ino;
mode_t st_mode;
nlink_t st_nlink;
uid_t st_uid;
gid_t st_gid;
dev_t st_rdev;
#ifndef _POSIX_SOURCE
struct timespec st_atimespec;
struct timespec st_mtimespec;
struct timespec st_ctimespec;
#else
time_t st_atime;
long st_atimensec;
time_t st_mtime;
long st_mtimensec;
time_t st_ctime;
long st_ctimensec;
#endif
off_t st_size;
int64_t st_blocks;
u_int32_t st_blksize;
u_int32_t st_flags;
u_int32_t st_gen;
int32_t st_lspare;
int64_t st_qspare[2];
};
"""
_fields_ = [
("st_dev", c_ulong),
("st_ino", c_ulong),
("st_mode", c_ushort),
("st_nlink", c_uint),
("st_uid", c_uint),
("st_gid", c_uint),
("st_rdev", c_ulong),
("st_atime", c_longlong),
("st_atimendesc", c_long),
("st_mtime", c_longlong),
("st_mtimendesc", c_long),
("st_ctime", c_longlong),
("st_ctimendesc", c_long),
("st_size", c_ulonglong),
("st_blocks", c_int64),
("st_blksize", c_uint32),
("st_flags", c_uint32),
("st_gen", c_uint32),
("st_lspare", c_int32),
("st_qspare", POINTER(c_int64) * 2),
]
# stat success
path = create_string_buffer(b"/etc/passwd")
st = Stat()
ret = stat(path, byref(st))
assert ret == 0
# if stat fail, check errno
path = create_string_buffer(b"&%$#@!")
st = Stat()
ret = stat(path, byref(st))
if ret != 0:
errno = get_errno() # get errno
errmsg = "stat({}) failed. {}".format(path.raw, os.strerror(errno))
raise OSError(errno, errmsg)
output:

.. code-block:: console
$ python err_handling.py # python2
Traceback (most recent call last):
File "err_handling.py", line 85, in <module>
raise OSError(errno_, errmsg)
OSError: [Errno 2] stat(&%$#@!) failed. No such file or directory
$ python3 err_handling.py # python3
Traceback (most recent call last):
File "err_handling.py", line 85, in <module>
raise OSError(errno_, errmsg)
FileNotFoundError: [Errno 2] stat(b'&%$#@!\x00') failed. No such file or directory

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