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:
- 传递给 CodeType 的巨大参数列表
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。FunctionType
help( 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, {} )