[Python-Dev] Let's just keep lambda

Thu Feb 9 19:24:43 CET 2006

On 2006年2月09日 17:39:31 +0100, =?ISO-8859-1?Q?=22Martin_v=2E_L=F6wis=22?= <martin at v.loewis.de> wrote:
>Jiwon Seo wrote:
>> Apparently, simplest example is,
>>>> collection.visit(lambda x: print x)
>>Ok. I remotely recall Guido suggesting that print should become
>a function.
>Even so, that one is so trivial to define (other than the >> part):
 >>> import sys
 >>> def printfun(*args): sys.stdout.write(' '.join(map(str,args))+'\n')
 ...
 >>> lamb = lambda x: printfun(x)
 >>>
 >>> lamb(123)
 123
 >>> printfun('How', 'about', 'that?')
 How about that?
Also the quasi-C variant:
 >>> def printf(fmt, *args): sys.stdout.write(fmt%args)
 ...
 >>> (lambda x: printf('How about this: %s', x))('-- also a function\n(no \\n here ;-) ')
 How about this: -- also a function
 (no \n here ;-) >>>
>It's not a specific example though: what precise library provides
>the visit method?
>>> which currently is not possible. Another example is,
>>>> map(lambda x: if odd(x): return 1
>> else: return 0,
>> listOfNumbers)
>>Hmm. What's wrong with
>>map(odd, listOfNumbers)
>>or, if you really need ints:
>>map(lambda x:int(odd(x)), listOfNumbers)
>>> Also, anything with exception handling code can't be without explicit
>> function definition.
>>>> collection.visit(lambda x: try: foo(x); except SomeError: error("error
>> message"))
>>That's not a specific example.
> >>> (lambda : """
 ... I will say that the multi-line part
 ... of the argument against lambda suites
 ... is bogus, though ;-)
 ... """)(
 ... ).splitlines(
 ... )[-1].split()[1].capitalize(
 ... ).rstrip(',')+'! (though this is ridiculous ;-)'
 'Bogus! (though this is ridiculous ;-)'
And, as you know, you can abuse the heck out of lambda (obviously this is
ridiculous**2 avoidance of external def)
 >>> lamb = lambda x: eval(compile("""if 1:
 ... def f(x):
 ... try: return 'zero one two three'.split()[x]
 ... except Exception,e:return 'No name for %r -- %s:%s'%(x,e.__class__.__name__, e)
 ... """,'','exec')) or locals()['f'](x)
 >>> lamb(2)
 'two'
 >>> lamb(0)
 'zero'
 >>> lamb(4)
 'No name for 4 -- IndexError:list index out of range'
 >>> lamb('x')
 "No name for 'x' -- TypeError:list indices must be integers"
But would e.g. [1]
 collection.visit(lambda x:: # double ':' to signify suite start
 try: return 'zero one two three'.split()[x]
 except Exception,e:return 'No name for %r -- %s:%s'%(x,e.__class__.__name__, e)
 )
be so bad an "improvement"? Search your heart for the purest answer ;-)
(requires enclosing parens, and suite ends on closing ')' and if multiline,
the first line after the :: defines the indent-one left edge, and explicit
return of value required after ::).
[1] (using the function body above just as example, not saying it makes sense for collection.visit)
Regards,
Bengt Richter

[Python-Dev] Let's just *keep* lambda

[Python-Dev] Let's just keep lambda