如何在Python中调用代码对象 [英] How to call code objects in Python

问题描述

当我掌握一个代码对象时(通过诸如.func_code之类的内部对象)，有什么方法可以调用这段代码?简单地调用它是行不通的:

When I get hold of a code object (via internals like .func_code), is there any way of calling this piece of code? Simply calling it does not work:

def f(): pass

f.func_code()

产生

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'code' object is not callable

当您想对嵌套函数进行单元测试时，这会派上用场:

This can come in handy when you like to unit-test a nested function:

def f():
  def g():
    return 3
  f.x = g
  return g() + 1

f.func_code.co_consts[1]

产生

<code object g at 0x7f123991b930, file "<stdin>", line 2>

当然，这段代码仍需要上下文等，但这不是我的问题.

Of course, this piece of code still needs a context etc. but that's not my question here.

推荐答案

一个人可以eval()或exec他们.

如果它们具有 free变量(例如，对于嵌套函数的代码，其外部函数在嵌套函数之前定义了局部变量)，则这是不可能直接实现的(eval或exec提高在这种情况下为TypeError.

If they have free variables (e. g. for the code of nested functions whose outer function has local variables defined before the nested function), this is not directly possible (eval or exec raise a TypeError in this case).

此外，也无法直接将参数传递给代码.

Also, passing arguments to the code is not directly possible.

但是可以为给定的代码动态创建包装函数.通常可以调用此函数(使用f(…))，以通常的方式传递参数.这是使用types.FunctionType完成的.要获得对 free变量的引用，必须使用技巧以获取Python期望的正确数据类型.有关示例，请参见下面的代码:

But one can create a wrapping function for the given code on-the-fly. This function can normally be called (using f(…)), passing arguments in the usual way. This is done using types.FunctionType. To achieve references to free variables, one must use a trick in order to get the correct data type as Python expects it. See the code below for an example:

def f(v1=1):
  v2 = 2
  def g(v3=4):
    return v1 + v2 + v3 + 8
  return g() + 16

def freeVar(val):
  def nested():
    return val
  return nested.__closure__[0]

def nested(outer, innerName, **freeVars):
  if isinstance(outer, (types.FunctionType, types.MethodType)):
    outer = outer.func_code
  for const in outer.co_consts:
    if isinstance(const, types.CodeType) and const.co_name == innerName:
      return types.FunctionType(const, globals(), None, None, tuple(
          freeVar(freeVars[name]) for name in const.co_freevars))

nestedG = nested(f, 'g', v1=1, v2=2)
print nestedG(4)  # will print 15

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