7

如果我有这个功能，我应该怎么做才能用我自己的自定义版本替换内部功能？

def foo():
    def bar():
        # I want to change this
        pass

    # here starts a long list of functions I want to keep unchanged
    def baz():
        pass

使用类很容易覆盖方法。不过，我不知道如何使用嵌套函数来做到这一点。更改foo为类（或其他任何东西）不是一种选择，因为它来自我无法修改的给定导入模块。

4

2 回答 2

11

这是一种方法，通过破解函数内部来创建一个“做正确的事情”的新 foo。（如@DSM 所述）。不幸的是，我们不能直接跳入foo函数并弄乱它的内部结构，因为它们大多被标记为只读，所以我们要做的就是修改我们手动构建的副本。

# Here's the original function
def foo():
  def bar():
    print("    In bar orig")
  def baz():
    print("  Calling bar from baz")
    bar()
  print("Foo calling bar:")
  bar()
  print("Foo calling baz:")
  baz()

# Here's using it
foo()

# Now lets override the bar function

import types

# This is our replacement function
def my_bar():
  print("   Woo hoo I'm the bar override")

# This creates a new code object used by our new foo function 
# based on the old foo functions code object.
foocode = types.CodeType(
    foo.func_code.co_argcount,
    foo.func_code.co_nlocals,
    foo.func_code.co_stacksize,
    foo.func_code.co_flags,
    foo.func_code.co_code,
    # This tuple is a new version of foo.func_code.co_consts
    # NOTE: Don't get this wrong or you will crash python.
    ( 
       foo.func_code.co_consts[0],
       my_bar.func_code,
       foo.func_code.co_consts[2],
       foo.func_code.co_consts[3],
       foo.func_code.co_consts[4]
    ),
    foo.func_code.co_names,
    foo.func_code.co_varnames,
    foo.func_code.co_filename,
    foo.func_code.co_name,
    foo.func_code.co_firstlineno,
    foo.func_code.co_lnotab,
    foo.func_code.co_freevars,
    foo.func_code.co_cellvars )

# This is the new function we're replacing foo with
# using our new code.
foo = types.FunctionType( foocode , {})

# Now use it
foo()

我很确定它不会涵盖所有情况。但它适用于示例（对我来说是旧的 python 2.5.1 ）

可以做一些整理的丑陋部分是：

  1. 传递给 CodeType 的巨大参数列表
  2. co_consts由仅覆盖一个成员构成的丑陋元组。所有信息都在 co_consts 中以确定替换哪个 - 所以更智能的函数可以做到这一点。我使用print( foo.func_code.co_consts ).

您可以使用解释器命令找到有关CodeType和的一些信息。FunctionTypehelp( types.CodeType )

更新：我觉得这太丑了，所以我构建了一个辅助函数来让它更漂亮。使用助手，您可以编写：

# Use our function to get a new version of foo with "bar" replaced by mybar    
foo = monkey_patch_fn( foo, "bar", my_bar )

# Check it works
foo()

这是 的实现monkey_patch_fn：

# Returns a copy of original_fn with its internal function
# called name replaced with new_fn.
def monkey_patch_fn( original_fn, name, new_fn ):

  #Little helper function to pick out the correct constant
  def fix_consts(x):
    if x==None: return None
    try:
      if x.co_name == name:
        return new_fn.func_code
    except AttributeError, e:
        pass
    return x

  original_code = original_fn.func_code
  new_consts = tuple( map( fix_consts, original_code.co_consts ) )
  code_type_args = [
     "co_argcount", "co_nlocals", "co_stacksize", "co_flags", "co_code",
     "co_consts", "co_names", "co_varnames", "co_filename", "co_name",
     "co_firstlineno", "co_lnotab", "co_freevars", "co_cellvars" ]

  new_code = types.CodeType(
     *[ ( getattr(original_code,x) if x!="co_consts" else new_consts )
        for x in code_type_args ] )
  return types.FunctionType( new_code, {} )
于 2012-08-11T05:07:29.523 回答
3

您可以将其作为可选参数传入

def foo(bar=None):
    def _bar():
        # I want to change this
        pass
    if bar is None:
        bar = _bar
于 2012-08-11T03:06:57.273 回答