get the name of lambda

[George Yoshida]

Just out of curiosity, is there any way to get the name of a
lambda expression? Lambdas are anonymous functions, so it's a
stupid idea to get the name of it. But if it's possible, how
could I?

Let's take a simple example:
foo = lambda:None

foo.__name__(or foo.func_name) returns '<lambda>'.
I'm looking for a way to return 'foo', instead of '<lambda>'.

Thanks in advance.

-- George

[Michael Hoffman]

Re: get the name of lambda

George Yoshida wrote:
[color=blue]
> Just out of curiosity, is there any way to get the name of a
> lambda expression? Lambdas are anonymous functions, so it's a
> stupid idea to get the name of it. But if it's possible, how
> could I?
>
> Let's take a simple example:
> foo = lambda:None
>
> foo.__name__(or foo.func_name) returns '<lambda>'.
> I'm looking for a way to return 'foo', instead of '<lambda>'.[/color]

But you already know that it is called 'foo'! :)

Anyway I don't think it has anything to do with lambda:
[color=blue][color=green][color=darkred]
>>> def x(): pass[/color][/color][/color]
....[color=blue][color=green][color=darkred]
>>> y = x
>>> y.__name__[/color][/color][/color]
'x'

IIRC, in 2.4 you can set the func_name attribute so you could set up a
decorator to set the name for you. Or if you want to be fancy you could
even set up a metaclass that automatically renames all the lambda
functions it finds in a class.

But why?
--
Michael Hoffman

[George Yoshida]

Re: get the name of lambda


Michael Hoffman wrote:
[color=blue]
> Anyway I don't think it has anything to do with lambda:
>[color=green][color=darkred]
> >>> def x(): pass[/color][/color]
> ...[color=green][color=darkred]
> >>> y = x
> >>> y.__name__[/color][/color]
> 'x'
>
> IIRC, in 2.4 you can set the func_name attribute so you could set up a
> decorator to set the name for you. Or if you want to be fancy you could
> even set up a metaclass that automatically renames all the lambda
> functions it finds in a class.[/color]

I haven't had a chance to play with decorators, but I'll give
it a try. In any case, I don't need a fancy way.
The simpler, the better.
[color=blue]
> But why?[/color]

I implemented a function in several ways(using recursion,
lambda, etc) and benchmarked them. In that script, I needed
to display function names, along with ellapsed time.

I was doing something like:

for func in (func1, func2, func3):
print func.func_name
print measure_ellapse d_time(func)

and get hit by lambda!

-- George

[Terry Reedy]

Re: get the name of lambda


"George Yoshida" <ml@dynkin.co m> wrote in message
news:ckr59p$1ep o$1@dojima-n0.hi-ho.ne.jp...[color=blue]
> Just out of curiosity, is there any way to get the name of a
> lambda expression? Lambdas are anonymous functions, so it's a
> stupid idea to get the name of it. But if it's possible, how
> could I?
>
> Let's take a simple example:
> foo = lambda:None
>
> foo.__name__(or foo.func_name) returns '<lambda>'.
> I'm looking for a way to return 'foo', instead of '<lambda>'.[/color]

Use 'def foo: return None' instead. This is precisely why a 'name = lambda
....' statement is inferior to a def statement.

[and in followup][color=blue]
> I implemented a function in several ways(using recursion,
> lambda, etc) and benchmarked them. In that script, I needed
> to display function names, along with ellapsed time.[/color]

So use a def instead of lambda. Only use lambda when you have an
expression to return and *do not need* a name to display. Python is not
Lisp ;-)

Terry J. Reedy

[Michael Hoffman]

Re: get the name of lambda

George Yoshida wrote:
[color=blue]
> I implemented a function in several ways(using recursion,
> lambda, etc) and benchmarked them. In that script, I needed
> to display function names, along with ellapsed time.[/color]

To be honest, I think munging the func_name attribute is a silly way to
get what you want :)
[color=blue]
> I was doing something like:
>
> for func in (func1, func2, func3):
> print func.func_name
> print measure_ellapse d_time(func)[/color]

How about:

funcs = dict(func1=func 1, func2=func2, func3=lambda: None)
for name, func in funcs.iteritems ():
print name
print measure_elapsed _time(func)
--
Michael Hoffman

[Piet van Oostrum]

Re: get the name of lambda

>>>>> George Yoshida <ml@dynkin.co m> (GY) wrote:

GY> Just out of curiosity, is there any way to get the name of a
GY> lambda expression? Lambdas are anonymous functions, so it's a
GY> stupid idea to get the name of it. But if it's possible, how
GY> could I?

You already said it: it's a stupid idea. Anonymous means: having no name,
so what is the name of an anonymous thing supposed to be.

GY> Let's take a simple example:
GY> foo = lambda:None

In your example foo is not the name of the lambda. It is just a variable
whose value is the lambda expression.

--
Piet van Oostrum <piet@cs.uu.n l>
URL: http://www.cs.uu.nl/~piet [PGP]
Private email: P.van.Oostrum@h ccnet.nl

[Tim Roberts]

Re: get the name of lambda

George Yoshida <ml@dynkin.co m> wrote:
[color=blue]
>Just out of curiosity, is there any way to get the name of a
>lambda expression? Lambdas are anonymous functions, so it's a
>stupid idea to get the name of it. But if it's possible, how
>could I?
>
>Let's take a simple example:
> foo = lambda:None
>
>foo.__name__(o r foo.func_name) returns '<lambda>'.
>I'm looking for a way to return 'foo', instead of '<lambda>'.[/color]

Can't be done. "foo" is just a name of a reference to something. The
lambda function has no idea that there happens to be a name called "foo"
that is bound to it. Consider this:

foo = boo = doo = lambda:None

def printMyName(zip py):
print zippy.__name__

printMyName( foo )
printMyName( boo )
printMyName( doo )

printMyName will get called 3 times with the exact same object. Inside
printMyName, would you expect the first call to print "foo"? Why not
"zippy"?
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.