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Let's Talk About Lambda Functions!

Alex Martelli aleax at aleax.it
Fri Jul 26 17:26:23 EDT 2002 
Paul Rubin wrote:

> "Britt A. Green" <python at experimentzero.org> writes:
>> So I know what lambda functions are, they're syntax and how they're used.
>> However I'm not sure *why* one would use a lambda function. What's the
>> advantage that they offer over a regular function?
> 
> You can use them inside other expressions, e.g. suppose you want to
> sort a bunch of strings starting with the second letter:
> 
>    a = ['apple', 'banana', 'pear', 'watermelon']
>    a.sort(lambda x,y: cmp(x[1],y[1]))
> 
> => ['banana', 'watermelon', 'pear', 'apple']
> 
> Without lambda, you'd have to define a separate named function:

Without lambda, you might be more tempted to do it right (a la DSU):

aux = [ (x[1], x) for x in a ]
aux.sort()
a[:] = [ x for __, x in aux ]

When you're sorting 4 items, it doesn't matter, but try -- not a
huge number -- just 400, say.


> There's a middle ground that says the name "lambda" (which comes from
> Lisp) wasn't a good choice and another name should have been used
> instead, like maybe 'func', which does the same thing.  I guess that's
> reasonable.  I'm used to lambda from Lisp but another name would
> probably be less scary to non-Lisp-users.

It's not an issue of syntax sugar as superficial as what keyword to
use.  A REAL lambda, by any other name -- the ability to package up
ANY chunk of code, not just an expression -- might add power enough
to justify its existence.  Today's lambda's just deadweight.  And I
do _not_ say that as a "non-Lisp-user" (though it's been a LONG time
since I last used Lisp, or Scheme for that matter, in production use).


Alex
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