[Python-ideas] a new lambda syntax

[Steven D'Aprano]

On Tue, 20 Oct 2009 09:33:48 am Michael Foord wrote:
> 2009/10/19 Oleg Broytman <phd at phd.pp.ru>
>
> > On Mon, Oct 19, 2009 at 10:28:58PM +0800, starwing wrote:
> > > Oleg Broytman ??????:
> > >>    Single-line lambdas are good enough,
> > >> and if you need more - just create a named function.
> > >
> > > BUT, why we need a name? just to process something or make
> > > decide, sometimes code itself is enough.
> >
> >    A multiline function is certainly not a simple piece of code; it
> > requires documentation - docstring, comments - and the name is a
> > part of the documentation.
>
> Having used languages that allow multiline anonymous functions (C#,
> Javascript) I have to say that they *can* improve the readability of
> code. 

Given the difficulty in testing such anonymous functions, what do they 
do to the correctness of programs?



> Being forced to define functions ahead of where they belong in 
> the logical flow of the program is not a feature of Python but a
> restriction.

I don't see that this restriction is worth the hours and hours people 
have spent on it. If I have code like this:


function(1, None, True, {  # define an anonymous dict
  'a': set([1, 2, 4, 8, ...], 
  'b': set([2, 4, 6, 9, 12, 16, 20, ...], 
  'c': set([1234, 1342, 1432, ...], 
  ...
  'z': set([12, 99, 151, 153, 745, ...])
  }, flag, count=4, parrot='red')

with a complicated data argument, then I can write it as an anonymous 
variable, but it actually hurts readability to do so. There's no 
problem with creating an anonymous dict of any complexity I like, but 
for readability and correctness I'm better off pulling it out of the 
function call and giving it a name:

d = {
  'a': set([1, 2, 4, 16, 128, ...], 
  'b': set([2, 4, 6, 9, 12, 16, 20, ...], 
  'c': set([1234, 1342, 1432, ...], 
  ...
  'z': set([12, 99, 151, 153, 745, ...])
  }
# print d
function(1, None, True, d, flag, count=4, parrot='red')

In fact, if it's that complicated, I'm better off creating a function to 
generate it, so I can test it:

function(1, None, True, d_factory(), flag, count=4, parrot='red')


My point is that when it comes to data, we have anonymous data that is 
easy and straightforward to define, and yet we *still* prefer to give 
data names and define it ahead of where we use it. So why is code 
different? Why does defining code ahead of where you use it such a bad 
thing that the lambda restriction generates so much attention?



-- 
Steven D'Aprano