replace 'apply' with extended call

Peter Otten __peter__ at web.de
Mon Oct 25 17:15:34 CEST 2004


Alan G Isaac wrote:

> 
> "Andrew Dalke" <adalke at mindspring.com> wrote in message
> news:b61fd.1486$kM.997 at newsread3.news.pas.earthlink.net...
>> How about a solution which replaces the 'map' with a
>> list comprehension?
>> def apply_each(fns, args = []):
>>    return [fn(*args) for fn in fns]
>> Conversion to lambda form is trivial for this case but I
>> figured if you're going to name it, why use a lambda?
> 
> 
> This raises another (newbie) question that I had.
> Take a trivial example:
> 
> from operator import truth
> bool1 = lambda lst: map(truth, lst)
> def bool2(lst): return map(truth,lst)
> def bool3(lst): return [truth(_) for _ in lst]
> 
> To my eyes, the most natural is bool2.
> I would never have considered bool1 if
> I had not come across it in the Merz book,
> but it is both shortest and clear.
> I include bool3 just for comparison: I think
> the way in which it is harder to read illustrates
> the usefulness of 'map'.
> 
> So, are there any obvious considerations when
> making a choice among these.  In particular,
> why might someone prefer the style in bool1?

I agree with you that using lambda is bad style for defining a named
function. I also prefer map() over list comprehensions if the expression is
a simple call to a predefined function, but a list comprehension is much
more flexible as it allows for expressions instead of function calls and
covers the functionality of filter() and map() in one pass. Personally, I
would just use the inline version of bool2, i. e. write

>>> map(bool, ["", [], 0, 0.0])
[False, False, False, False]

directly without bothering to define a function first. I didn't know about
truth(), but it seems to be equivalent to bool() - so why bother with the
import?

Peter





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