map in Python

[Pierre Barbier de Reuille]

You have three ways to do what you want :

First wayt is to use lambda. Then, you want to write :

 >>> map(lambda x: re.sub("[a-z]", "", x), test)

Second is to use regular named function :

 >>> def remove_letters( s ):
...   re.sub("[a-z]", "", s)
 >>> map(remove_letters, test)

A third way would be to use the "pseudo-currying" described there : 
http://www.python.org/moin/PythonDecoratorLibrary

In fact, you need a small generalisation :

 >>> class curried(object):
...   def __init__(self, func, *a, **kw):
...     self.func = func
...     self.args = a
...     self.kwords = kw
...   def __call__(self, *a, **kw):
...     args = self.args + a
...     kwords = dict(self.kwords)
...     kwords.update(kw)
...     if len(args)+len(kwords) < self.func.func_code.co_argcount:
...       return curried(self.func, *args, **kwords)
...     else:
...       return self.func(*args, **kwords)

The difference is you can handle the kwords with that version !
Then you want to write this :

 >>> curried_sub = curried(re.sub)
 >>> map(curried_sub("[a-z]", "", count=0), test)

My opinion is : the simplest and best solution more "pythonic" is the 
second one ! The third one is interesting but work only for functions 
written in Python ! (Hopefully the re.sub function is written in 
Python). The biggest problem with the first one is that lambda are 
planned to disappear in future Python versions ...

Pierre

Stu a écrit :
> I have recently switched over to Python from Perl. I want to do
> something like this in Python:
> 
> @test = ("a1", "a2", "a3");
> map {s/[a-z]//g} @test;
> print @test;
> 
> However, I take it there is no equivalent to $_ in Python. But in that
> case how does map pass the elements of a sequence to a function? I
> tried the following, but it doesn't work because the interpreter
> complains about a missing third argument to re.sub.
> 
> import re
> test = ["a1", "a2", "a3"]
> map(re.sub("[a-z]", ""), test)
> print test
> Thanks in advance.
> 
> Regards,
> Stuart <stuart AT zapata DOT org>
>