Nested Function Question

[GZ]

Hi,

I am reading the documentation of functools.partial (http://
docs.python.org/library/functools.html#functools.partial) and found
the following 'reference implementation' of functools.partial.

def partial(func, *args, **keywords):
def newfunc(*fargs, **fkeywords):
newkeywords = keywords.copy()
newkeywords.update(fkeywords)
return func(*(args + fargs), **newkeywords)
newfunc.func = func
newfunc.args = args
newfunc.keywords = keywords
return newfunc

I don't understand why the below 3 lines are needed:

newfunc.func = func
newfunc.args = args
newfunc.keywords = keywords


It is as if they are trying to prevent garbage collection, but I don't
get why it is needed. As long as something holds reference to newfunc,
because it in turn references keywords and args, nothing will be
freed. If nothing is referencing newfunc, then everything should be
freed.

Thanks,
GZ

 

[Ian Kelly]

Hi,

I am reading the documentation of functools.partial (http://
docs.python.org/library/functools.html#functools.partial) and found
the following 'reference implementation' of functools.partial.

def partial(func, *args, **keywords):
   def newfunc(*fargs, **fkeywords):
       newkeywords = keywords.copy()
       newkeywords.update(fkeywords)
       return func(*(args + fargs), **newkeywords)
   newfunc.func = func
   newfunc.args = args
   newfunc.keywords = keywords
   return newfunc

I don't understand why the below 3 lines are needed:

   newfunc.func = func
   newfunc.args = args
   newfunc.keywords = keywords


It is as if they are trying to prevent garbage collection, but I don't
get why it is needed. As long as something holds reference to newfunc,
because it in turn references keywords and args, nothing will be
freed. If nothing is referencing newfunc, then everything should be
freed.

They exist for introspection. The partial object has to store the
function and arguments it was passed so that it can call it later, so
as long as they're being stored anyway, why not make them visible?

 

[David Robinow]

They exist for introspection.  The partial object has to store the
function and arguments it was passed so that it can call it later, so
as long as they're being stored anyway, why not make them visible?

I tend toward the minimalist end of the spectrum when it comes to code
commenting, but it seems to me this would be a good place for a few
words of explanation.

 

[88888 Dihedral]

GZæ–¼ 2012å¹´1月7日星期六UTC+8上åˆ5時46分16秒寫é“：

Hi,

I am reading the documentation of functools.partial (http://
docs.python.org/library/functools.html#functools.partial) and found
the following 'reference implementation' of functools.partial.

def partial(func, *args, **keywords):
def newfunc(*fargs, **fkeywords):
newkeywords = keywords.copy()
newkeywords.update(fkeywords)
return func(*(args + fargs), **newkeywords)
newfunc.func = func
newfunc.args = args
newfunc.keywords = keywords
return newfunc

I don't understand why the below 3 lines are needed:

newfunc.func = func
newfunc.args = args
newfunc.keywords = keywords


It is as if they are trying to prevent garbage collection, but I don't
get why it is needed. As long as something holds reference to newfunc,
because it in turn references keywords and args, nothing will be
freed. If nothing is referencing newfunc, then everything should be
freed.

Thanks,
GZ

This is used to produce a new function with some default parameters fixed
of an old function that requires many parameters in the caller part.