上一篇里的LAME項(xiàng)目已經(jīng)展示了python如何與C語言交互，但程序仍不夠理想，在python這一端僅僅是傳遞源文件和目標(biāo)文件的路徑，再調(diào)用C模塊的encode方法來進(jìn)行編碼，但問題在于你無法控制encode函數(shù)，比如你想編碼的源文件如果不是原始數(shù)據(jù)，而是wav文件或者其他格式呢？對于這個(gè)問題，有兩種方法可以選擇，一種模仿前面的C模塊，在你的Python代碼中讀取數(shù)據(jù)，并將數(shù)據(jù)塊逐個(gè)傳遞給encode函數(shù)，另一種方法是你傳進(jìn)去一個(gè)對象，這個(gè)對象帶有一個(gè)read方法，這樣你就可以在C模塊里直接調(diào)用它的read方法來讀取其數(shù)據(jù)。 聽起來好像第二種更加面向?qū)ο?#xff0c;但實(shí)際上第一種方法反而是更為合適的選擇，因?yàn)樗鼮殪`活,下面我們就在上一篇的基礎(chǔ)上,利用第一種思路對其進(jìn)行改造。在這種新方法中，我們需要多次調(diào)用C模塊的函數(shù)，類似于將其視為類的方法。可C語言是不支持類的，因此需要將狀態(tài)信息存儲在某個(gè)地方。除此以外，我們需要將“類”暴露給外部的Python程序，使其能創(chuàng)建“類“的實(shí)例，并調(diào)用它的方法。在“類對象“的內(nèi)部我們則將其寫數(shù)據(jù)的文件信息儲存在”對象“的狀態(tài)中。聽上去就是一種面向?qū)ο蟮姆椒?#xff0c;不是嗎？首先,遵循"測試先行"的原則,先來看我們改造后的Python這一端,你可以每次讀取音頻源文件的一個(gè)數(shù)據(jù)塊,將其轉(zhuǎn)遞給Encoder對象的encode方法,這樣無論你的源文件是何種格式,你都可以在Encoder中進(jìn)行自由的控制,示例代碼如下:代碼import?clame

INBUFSIZE?=?4096

if?__name__?==?'__main__':
????encoder?=?clame.Encoder('test.mp3')
????input?=?file('test.raw',?'rb')
????data?=?input.read(INBUFSIZE)

????while?data?!=?'':
????????encoder.encode(data)
????????data?=?input.read(INBUFSIZE)
????input.close()
????encoder.close()

?再來看C擴(kuò)展模塊這一端，下面是完整的代碼：

代碼#include?<Python.h>
#include?<lame.h>

typedef?struct?{
????PyObject_HEAD
????FILE*?outfp;
????lame_global_flags*?gfp;
}clame_EncoderObject;

static?PyObject*?Encoder_new(PyTypeObject*?type,?PyObject*?args,?PyObject*?kw)?{
????clame_EncoderObject*?self?=?(clame_EncoderObject*?)type->tp_alloc(type,?0);
????self->outfp?=?NULL;
????self->gfp?=?NULL;
????return?(PyObject*)self;
}

static?void?Encoder_dealloc(clame_EncoderObject*?self)?{
????if?(self->gfp)?{
????????lame_close(self->gfp);
????}
????if?(self->outfp)?{
????????fclose(self->outfp);
????}
????self->ob_type->tp_free(self);
}

static?int?Encoder_init(clame_EncoderObject*?self,?PyObject*?args,?PyObject*?kw)?{
????char*?outPath;
????if?(!PyArg_ParseTuple(args,?"s",?&outPath))?{
????????return?-1;
????}
????if?(self->outfp?||?self->gfp)?{????
????????PyErr_SetString(PyExc_Exception,?"__init__?already?called");
????????return?-1;
????}
????self->outfp?=?fopen(outPath,?"wb");
????self->gfp?=?lame_init();
????lame_init_params(self->gfp);
????return?0;
}

static?PyObject*?Encoder_encode(clame_EncoderObject*?self,?PyObject*?args)?{
????char*?in_buffer;
????int?in_length;
????int?mp3_length;
????char*?mp3_buffer;
????int?mp3_bytes;
????if?(!(self->outfp?||?self->gfp))?{
????????PyErr_SetString(PyExc_Exception,?"encoder?not?open");
????????return?NULL;
????}
????if?(!PyArg_ParseTuple(args,?"s#",?&in_buffer,?&in_length))?{
????????return?NULL;
????}
????in_length?/=?2;
????mp3_length?=?(int)(1.25?*?in_length)?+?7200;
????mp3_buffer?=?(char*)malloc(mp3_length);
????if?(in_length?>?0)?{
????????mp3_bytes?=?lame_encode_buffer_interleaved(self->gfp,?(short*)in_buffer,?in_length/2,?mp3_buffer,?mp3_length);
????????if?(mp3_bytes?>?0)?{
????????????fwrite(mp3_buffer,?1,?mp3_bytes,?self->outfp);
????????}
????}
????free(mp3_buffer);
????Py_RETURN_NONE;
}

static?PyObject*?Encoder_close(clame_EncoderObject*?self)?{
????int?mp3_length;
????char*?mp3_buffer;
????int?mp3_bytes;
????if?(!(self->outfp?&&?self->gfp))?{
????????PyErr_SetString(PyExc_Exception,?"encoder?not?open");
????????return?NULL;
????}
????mp3_length?=?7200;
????mp3_buffer?=?(char*)malloc(mp3_length);
????mp3_bytes?=?lame_encode_flush(self->gfp,?mp3_buffer,?sizeof(mp3_buffer));
????if?(mp3_bytes?>?0)?{
????????fwrite(mp3_buffer,?1,?mp3_bytes,?self->outfp);????????
????}
????free(mp3_buffer);
????lame_close(self->gfp);
????self->gfp?=?NULL;
????fclose(self->outfp);
????self->outfp?=?NULL;
????Py_RETURN_NONE;
}

static?PyMethodDef?Encoder_methods[]?=?{
????{"encode",?(PyCFunction)Encoder_encode,?METH_VARARGS,?"encodes?and?writes?data?to?the?output?file."},
????{"close",?(PyCFunction)Encoder_close,?METH_NOARGS,?"close?the?output?file."},
????{NULL,?NULL,?0,?NULL}
};

static?PyTypeObject?clame_EncoderType?=?{
????PyObject_HEAD_INIT(NULL)
????0,????????????????????????????????????//?ob_size
????"clame.Encoder",????????????????????//?tp_name
????sizeof(clame_EncoderObject),????????//?tp_basicsize
????0,????????????????????????????????????//?tp_itemsize
????(destructor)Encoder_dealloc,????????//?tp_dealloc
????0,????????????????????????????????????//?tp_print
????0,????????????????????????????????????//?tp_getattr
????0,????????????????????????????????????//?tp_setattr
????0,????????????????????????????????????//?tp_compare
????0,????????????????????????????????????//?tp_repr
????0,????????????????????????????????????//?tp_as_number
????0,????????????????????????????????????//?tp_as_sequence
????0,????????????????????????????????????//?tp_as_mapping
????0,????????????????????????????????????//?tp_hash
????0,?????????????????????????????????????//?tp_call
????0,????????????????????????????????????//?tp_str
????0,????????????????????????????????????//?tp_getattro
????0,????????????????????????????????????//?tp_setattro
????0,????????????????????????????????????//?tp_as_buffer
????Py_TPFLAGS_DEFAULT,????????????????????//?tp_flags
????"My?first?encoder?object.",????????????//?tp_doc
????0,????????????????????????????????????//?tp_traverse
????0,????????????????????????????????????//?tp_clear
????0,????????????????????????????????????//?tp_richcompare
????0,????????????????????????????????????//?tp_weaklistoffset
????0,????????????????????????????????????//?tp_iter
????0,????????????????????????????????????//?tp_iternext
????Encoder_methods,????????????????????//?tp_methods
????0,????????????????????????????????????//?tp_members
????0,????????????????????????????????????//?tp_getset
????0,????????????????????????????????????//?tp_base
????0,????????????????????????????????????//?tp_dict
????0,????????????????????????????????????//?tp_descr_get
????0,????????????????????????????????????//?tp_descr_set
????0,????????????????????????????????????//?tp_dictoffset
????(initproc)Encoder_init,????????????????//?tp_init
????0,????????????????????????????????????//?tp_alloc
????Encoder_new,????????????????????????//?tp_new
????0,????????????????????????????????????//?tp_free
};

static?PyMethodDef?clame_methods[]?=?{????
????{NULL,?NULL,?0,?NULL}
};

PyMODINIT_FUNC?initclame()?{
????PyObject*?m;
????if?(PyType_Ready(&clame_EncoderType)?<?0)?{
????????return;
????
????m?=?Py_InitModule3("clame",?clame_methods,?"My?second?lame?module.");
????Py_INCREF(&clame_EncoderType);
????PyModule_AddObject(m,?"Encoder",?(PyObject*)?&clame_EncoderType);
}

編譯過程：

gcc?-shared?-I?/usr/include/python2.6?-I?/usr/local/include/lame?clame.c?-lmp3lame?-o?clame.so

首先定義了clame_EncoderObject結(jié)構(gòu)體，這個(gè)結(jié)構(gòu)體就是用來存儲狀態(tài)信息的，字段outfp用來存儲輸出文件，gfp則保存lame的狀態(tài)，可以用來檢查是否已經(jīng)是重復(fù)調(diào)用已經(jīng)調(diào)用過的函數(shù)了。

為了創(chuàng)建這個(gè)結(jié)構(gòu)體的一個(gè)新實(shí)例，我們需要定義Encoder_new函數(shù)，你可以把這個(gè)函數(shù)視為Python里的__new__方法，當(dāng)Python解釋器需要?jiǎng)?chuàng)建你定義的類型的新實(shí)例時(shí)就會去調(diào)用這個(gè)方法。在這個(gè)方法里沒作什么操作，僅僅是做初始化工作，把outfp和gfp都設(shè)置為NULL,此外，與Encoder_new函數(shù)對應(yīng)，還需要定義Encoder_dealloc方法來對實(shí)例進(jìn)行析構(gòu)，你可以把這個(gè)函數(shù)視為Python的__del__方法，clame_EncoderType結(jié)構(gòu)體則是真正定義了我們的Encoder對象，它的各個(gè)字段指定了_new,_close,_encode,_dealloc等方法。在initclame方法中，PyModuleObject則實(shí)際指定了在Python程序中使用的Encoder對象。?

?

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