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Re: "eval vs operator.methodcaller" - which is better?

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  Re: "eval vs operator.methodcaller" - which is better? Laxmikant Chitare <laxmikant.general@gmail.com> - 2013-03-18 19:28 +0530
    Re: "eval vs operator.methodcaller" - which is better? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-18 14:23 +0000

#41416 — Re: "eval vs operator.methodcaller" - which is better?

Aha, that was smart Chris. Thank you.

But this raises another question in my mind. What is the use case for
operator.methodcaller ?

On 3/18/13, Chris Angelico <rosuav@gmail.com> wrote:
> On Tue, Mar 19, 2013 at 12:30 AM, Laxmikant Chitare
> <laxmikant.general@gmail.com> wrote:
>> moduleName = 'mymodule'    #These two variables are read from conf file.
>> methodName = 'mymethod'
>>
>> import operator
>> myModule = __import__('mymodule')
>> myMethod = operator.methodcaller('mymethod')
>> val = myMethod(myModule)
>> print val
>
> Is there any reason not to do the obvious?
>
> val = myModule.__getattribute__(methodName)(... args ...)
>
> Works in 2.6 and 3.3, at least on the trivial example I tried.
>
> ChrisA
> --
> http://mail.python.org/mailman/listinfo/python-list
>

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#41426

On Mon, 18 Mar 2013 19:28:37 +0530, Laxmikant Chitare wrote:

> Aha, that was smart Chris. Thank you.
> 
> But this raises another question in my mind. What is the use case for
> operator.methodcaller ?


The use-case is mostly to allow people to write code in a functional 
style, if they so choose.

import operator
func = operator.methodcaller("spam")
items = map(func, [a, b, c, d])

is the functional-style equivalent of:

items = [obj.spam() for obj in [a, b, c, d]]

methodcaller makes a little more sense if you provide arguments:


func = operator.methodcaller("spam", 1, 2, None, "ham")
items = map(func, [a, b, c, d])

compared to:

items = [obj.spam(1, 2, None, "ham") for obj in [a, b, c, d]]


I expect that the methodcaller version will be very slightly faster in 
this case, since it doesn't have to parse the arguments every time the 
method is called.



-- 
Steven

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