python - python函数/方法调用有什么静态的吗？

Question

在asking a question about reflection我问:

Nice answer. But there is a difference between saying myobject.foo() and x = getattr(myobject, "foo"); x();. Even if it is only cosmetic. In the first the foo() is compiled in statically. In the second, the string could be produced any number of ways. – Joe 1 hour ago

哪个得到了答案:

Eh, potato / solanum tuberosum... in python, niether is statically compiled, so they are more or less equivalent. – SWeko 1 hour ago

我知道 Python 对象的成员存储在字典中并且一切都是动态的，但我假设给出以下代码:

class Thing():
  def m(self):
    pass

t = Thing()

生成 .pyc 时，以下代码将以某种方式进行静态编译:

t.m()

即编译器知道 m() 的地址，所以在运行时没有点绑定(bind)。那个或运行时将缓存后续查找。

而这总是涉及查字典:

meth = getattr(t, "m")
meth()

是否所有调用都被视为字典中的字符串查找？或者这两个示例实际上是相同的？

Answer 1

它们并不完全相同，但它们都是字典查找，如反汇编程序所示 dis.dis .

请特别注意 LOAD_ATTR 指令，它按名称动态查找属性。根据文档，它“将 TOS [堆栈顶部] 替换为 getattr(TOS, co_names[namei])”。

>>> from dis import dis
>>> dis(lambda: t.m())
  1           0 LOAD_GLOBAL              0 (t)
              3 LOAD_ATTR                1 (m)
              6 CALL_FUNCTION            0
              9 RETURN_VALUE        
>>> dis(lambda: getattr(t, 'm')())
  1           0 LOAD_GLOBAL              0 (getattr)
              3 LOAD_GLOBAL              1 (t)
              6 LOAD_CONST               0 ('m')
              9 CALL_FUNCTION            2
             12 CALL_FUNCTION            0
             15 RETURN_VALUE