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Source Code of Python

人生苦短,我用Python

解释器与 opcode

先创建一个 test.py 文件。

x = 1
y = 2
print(x + y)

IPython 中查看

In [2]: c = compile('test.py', 'test.py', 'exec')

In [3]: c.co_code
Out[3]: b'e\x00\x00j\x01\x00\x01d\x00\x00S'

IPython 中可以看到,c 有很多属性,这些属性都定义在 code.h 里:

/* Bytecode object */
typedef struct {
    PyObject_HEAD
    int co_argcount;                /* #arguments, except *args */
    int co_kwonlyargcount;  /* #keyword only arguments */
    int co_nlocals;         /* #local variables */
    int co_stacksize;               /* #entries needed for evaluation stack */
    int co_flags;           /* CO_..., see below */
    PyObject *co_code;              /* instruction opcodes */
    PyObject *co_consts;    /* list (constants used) */
    PyObject *co_names;             /* list of strings (names used) */
    PyObject *co_varnames;  /* tuple of strings (local variable names) */
    PyObject *co_freevars;  /* tuple of strings (free variable names) */
    PyObject *co_cellvars;      /* tuple of strings (cell variable names) */
    /* The rest aren't used in either hash or comparisons, except for
    co_name (used in both) and co_firstlineno (used only in
    comparisons).  This is done to preserve the name and line number
    for tracebacks and debuggers; otherwise, constant de-duplication
    would collapse identical functions/lambdas defined on different lines.
    */
    unsigned char *co_cell2arg; /* Maps cell vars which are arguments. */
    PyObject *co_filename;  /* unicode (where it was loaded from) */
    PyObject *co_name;              /* unicode (name, for reference) */
    int co_firstlineno;             /* first source line number */
    PyObject *co_lnotab;    /* string (encoding addr<->lineno mapping) See
                Objects/lnotab_notes.txt for details. */
    void *co_zombieframe;     /* for optimization only (see frameobject.c) */
    PyObject *co_weakreflist;   /* to support weakrefs to code objects */
} PyCodeObject;

属性对应如下:

属性 作用
co_code 字节码指令序列
co_consts 常量列表
co_names 符号序列
llll llllll

接着上面的例子,查看 co_code,字节码是以 byte 字符串的形式存在。通过查找 asciitable 可以看到不同的指令的含义。

In [3]: c.co_code
Out[3]: b'e\x00\x00j\x01\x00\x01d\x00\x00S'

In [4]: [i for i in c.co_code]
Out[4]: [101, 0, 0, 106, 1, 0, 1, 100, 0, 0, 83]

In [5]: [hex(i) for i in c.co_code]
Out[5]:
['0x65',
'0x0',
'0x0',
'0x6a',
'0x1',
'0x0',
'0x1',
'0x64',
'0x0',
'0x0',
'0x53']

opcode.h 中可以找到指令对应的定义,比如上面看到 101 对应 LOAD_NAME

利用 Python 提供的 dis 可以验证刚刚看到的指令。

$ python3 -m dis test.py
1           0 LOAD_CONST               0 (1)
            3 STORE_NAME               0 (a)

2           6 LOAD_CONST               1 (2)
            9 STORE_NAME               1 (b)

3           12 LOAD_NAME                2 (print)
            15 LOAD_NAME                0 (a)
            18 LOAD_NAME                1 (b)
            21 BINARY_ADD
            22 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
            25 POP_TOP
            26 LOAD_CONST               2 (None)
            29 RETURN_VALUE