Ideas for Python 3

[Peter Otten]

Josiah Carlson wrote:

> How about this for a manual page for lambda...
> 
> In other languages, Python's lambda would be considered an 'anonymous
> function', that is, a function that does not require a name.:
> 
>      >>> (lambda arg: arg*arg)(9)
>      81
> 
> Certainly you can give lambdas names with standard assignments.:
> 
>      >>> square = lambda arg: arg*arg
>      >>> square(9)
>      81
> 
> The equivalent function definition is below.:
> 
>      >>> def square(arg):
>      ...     return arg*arg
>      ...
>      >>> square(9)
>      81
> 
> Generally, lambdas are functions with a single expression in its body
> whose value is returned.  Just like normal function definitions, lambdas
> can take multiple arguments, contain keyword arguments, return any
> Python type, etc., as long as the function body is a single expression,
> and whose parameters match standard function definition syntax, the
> lambda is valid. (leave annotation and/or link to what an expression is)

I suggest that you submit the above as a patch for the tutorial
http://www.python.org/doc/current/tut/node6.html. Currently there is an
example with a nice trick which has nothing to do with lambda. Your more
straightforward example demonstrates how simple lambda really is.

> An ugly example of this is as follows.:
> 
>      >>> f = lambda a, b=1, *args, **kwargs: (a, b, args, kwargs)
>      >>> f(1,2,3,c=4)
>      (1, 2, (3,), {'c': 4})
> 
> Which is equivalent to:
> 
>      >>> def f(a, b=1, *args, **kwargs):
>      ...     return (a, b, args, kwargs)
>      ...
>      >>> f(1,2,3,c=4)
>      (1, 2, (3,), {'c': 4})

At this point of learning the language a newbie may or may not be
comfortable with the *args, **kw special arguments. As their usage is
completely orthogonal to functions/lambdas I wouldn't mention them here.

Peter