map in Python

[Stu]

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>

[Simon Brunning]

Re: map in Python

On 21 Jan 2005 04:25:27 -0800, Stu <stuart@zapata. org> wrote:[color=blue]
> 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[/color]

This what you want?
[color=blue][color=green][color=darkred]
>>> import re
>>> test = ["a1", "a2", "a3"]
>>> test = [re.sub("[a-z]", "", item) for item in test]
>>> test[/color][/color][/color]
['1', '2', '3']

--
Cheers,
Simon B,
simon@brunningo nline.net,

http://www.brunningonline.net/simon/blog/

[Simon Brunning]

Re: map in Python

On Fri, 21 Jan 2005 12:37:46 +0000, Simon Brunning
<simon.brunning @gmail.com> wrote:[color=blue]
> This what you want?
>[color=green][color=darkred]
> >>> import re
> >>> test = ["a1", "a2", "a3"]
> >>> test = [re.sub("[a-z]", "", item) for item in test]
> >>> test[/color][/color]
> ['1', '2', '3'][/color]

Or, if you *must* use map, you can do:
[color=blue][color=green][color=darkred]
>>> test = map(lambda item: re.sub("[a-z]", "", item), test)
>>> test[/color][/color][/color]
['1', '2', '3']

I much prefer the first list comprehension form myself, but reasonable
men can differ...

--
Cheers,
Simon B,
simon@brunningo nline.net,

http://www.brunningonline.net/simon/blog/

[Pierre Barbier de Reuille]

Re: map in Python

You have three ways to do what you want :

First wayt is to use lambda. Then, you want to write :
[color=blue][color=green][color=darkred]
>>> map(lambda x: re.sub("[a-z]", "", x), test)[/color][/color][/color]

Second is to use regular named function :
[color=blue][color=green][color=darkred]
>>> def remove_letters( s ):[/color][/color][/color]
.... re.sub("[a-z]", "", s)[color=blue][color=green][color=darkred]
>>> map(remove_lett ers, test)[/color][/color][/color]

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 :
[color=blue][color=green][color=darkred]
>>> class curried(object) :[/color][/color][/color]
.... 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.kword s)
.... kwords.update(k w)
.... if len(args)+len(k words) < self.func.func_ code.co_argcoun t:
.... return curried(self.fu nc, *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 :
[color=blue][color=green][color=darkred]
>>> curried_sub = curried(re.sub)
>>> map(curried_sub ("[a-z]", "", count=0), test)[/color][/color][/color]

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 :[color=blue]
> 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>
>[/color]