P.S. Re: Python newbie needs constructive suggestions

[Duncan Booth]

David G. Wonnacott wrote:

> In response to my question, ``What is the idiomatically appropriate
> Python way to pass, as a "function-type parameter", code that is most
> clearly written with a local variable?'', a number of you made very
> helpful suggestions, including the use of a default argument; if one
> wanted to give a name to the constant one in my original example,
> 
>    map(lambda x: x+1, [5, 17, 49.5])
> 
> one would write
> 
>    map(lambda x, one=1: x+one, [5, 17, 49.5])
> 
> I've been using this happily in several cases, but just discovered
> that (of course), the variable "x" is not in scope until the
> expression in the lambda, so if one wanted to, say, have a variable
> that was 3*x, one could NOT write
> 
>    map(lambda x, threex=3*x: x+threex, [5, 17, 49.5])
> 
> [obviously there are easier ways to find 4*x, but I'm trying to keep
> close to my simplified example].
> 
> I'll need to show the code to beginners, so I don't want to get into
> the complexity of using the more advanced solutions that were
> suggested (closures or callable classes), so I'm going to bail out in
> such cases and just not use an anonymous function here.
> 

Not using an anonymous function certainly sounds to me like the most 
"idiomatically appropriate Python way" to do this.

def fourx(x):
   threex = 3 * x
   return x + threex

map(fourx, [5, 17, 49.5])

The advantages over the lambda include the ability to use local variables 
and split the function naturally over multiple lines. Also you get to use a 
meaningful name to describe the function.