python中的code object

引入

看一段python代码，打印一个函数的__code__,返回的是一个code object，code object是什么，有哪些属性呢？

def f():
    pass
f.__code__
<code object f at 0x00000176FC4E8B30, file "", line 1>
dir(f.__code__)
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'co_argcount', 'co_cellvars', 'co_code', 'co_consts', 'co_filename', 'co_firstlineno', 'co_flags', 'co_freevars', 'co_kwonlyargcount', 'co_lnotab', 'co_name', 'co_names', 'co_nlocals', 'co_posonlyargcount', 'co_stacksize', 'co_varnames', 'replace']

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code object的各个属性的含义可以参考官方文档code object属性含义

概念

code object是一段可执行的python代码在CPython中的内部表示，包含一系列直接操作虚拟机内部状态的指令
可执行的python代码包括函数,模块,类,生成器表达式
当运行一段代码时，程序被解析，编译成字节码，并被CPython虚拟机执行

尝试

容易理解的几个

def f():
    pass


code = f.__code__
print(code.co_code)  # b'd\x00S\x00' 字节码
print(code.co_name)  # f 函数名
print(code.co_filename)  # D:\learn_py\code_object.py 文件名
print(code.co_lnotab)  # b'\x00\x01' encoded mapping of line numbers to bytecode indices 行号与字节码的映射
print(code.co_flags)  # 67 https://docs.python.org/3/library/inspect.html?highlight=__code__#inspect-module-co-flags
print(code.co_stacksize)  # 1 virtual machine stack space required 虚拟机需要的栈空间
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count

co_argcount 表示除keyword only arguments, * or ** args外的参数个数
co_posonlyargcount表示positional only arguments个数
co_kwonlyargcount表示keyword only arguments (not including ** arg)

def f(a, b=2, *args, **kwargs):
    pass


code = f.__code__

print(code.co_argcount)  # 2 number of arguments (not including keyword only arguments, * or ** args),不包括only keyword
print(code.co_posonlyargcount)  # 0 number of positional only arguments
print(code.co_kwonlyargcount)  # 0 number of keyword only arguments (not including ** arg)
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函数定义时可以用‘/’划分，将’/'前面的规定全为positional only arguments

def f(a, b=2, /, *args, **kwargs):
    pass


code = f.__code__

print(code.co_argcount)  # 2 number of arguments (not including keyword only arguments, * or ** args),不包括only keyword
print(code.co_posonlyargcount)  # 2 number of positional only arguments
print(code.co_kwonlyargcount)  # 0 number of keyword only arguments (not including ** arg)
f(1, 1)
f(1)
f(a=1)  # 报错TypeError: f() missing 1 required positional argument: 'a'
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同时还可以用‘‘划分,’'后面的全部都是keyword only arguments

def f(a, *, b=2, **kwargs):
    pass


code = f.__code__

print(code.co_argcount)  # 1 number of arguments (not including keyword only arguments, * or ** args),不包括only keyword
print(code.co_posonlyargcount)  # 0 number of positional only arguments
print(code.co_kwonlyargcount)  # 1 number of keyword only arguments (not including ** arg)

f(a=1)
f(1)
f(1, 2)  # TypeError: f() takes 1 positional argument but 2 were given

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names

def f(a):
    import math as m
    b = a.attr
    c = 2
    e = 3
    f1 = "xxxx"
    d1 = c + b
    return b
import dis
dis.dis(f)

code = f.__code__
print(code.co_nlocals)  # 7 局部变量的数量,等于co_varnames的size
print(code.co_varnames)  # ('a', 'm', 'b', 'c', 'e', 'f1', 'd1') local variables 的string
print(code.co_names)  # ('math', 'attr') 除了co_varnames，co_cellvars， co_freevars之外的其他
print(code.co_cellvars)
print(code.co_freevars)
print(code.co_consts)  # (None, 0, 2, 3, 'xxxx') 出现的常量如数字，字符串

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co_cellvars和co_freevars常在闭包中成对出现，co_freevars表示用到了scope之外的变量，co_cellvars表示变量被其他scope使用

def g():
    a = {}

    def f():
        pass
    return f


code = g.__code__
print(code.co_varnames)
print(code.co_cellvars)
print(code.co_freevars)
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def g():
    a = {}

    def f():
        a["name"] = "haha"
        pass
    return f


code = g.__code__
print(code.co_varnames)  # ('f',)
print(code.co_cellvars)  # ('a',)
print(code.co_freevars)
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def g():
    a = {}

    def f():
        a["name"] = "haha"
        pass
    return f


code = g().__code__
print(code.co_varnames)
print(code.co_cellvars)
print(code.co_freevars)  # ('a',)
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