# Help with map python 2

Sayth Renshaw flebber.crue at gmail.com
Sun Jan 4 22:22:19 CET 2015

```Thank you for those solutions so varied. Am going to have a party with them
to see what works best for me.

Strange is there a way too use lousy comprehension without returning just
the matching odd values?

Sayth

On Mon, 5 Jan 2015 5:06 AM Dan Stromberg <drsalists at gmail.com> wrote:

> I'm partial to:
>
> #!/usr/local/cpython-3.4/bin/python
>
> def gen_series(top=None):
>     '''
>     Generate the numbers from 2 to top, with alternating signs.
>     If top is None, generate forever.
>     If top is an integer, generate from 2 to top.
>     '''
>     sign = 1
>     if top is None:
>         number = 2
>         while True:
>             yield number * sign
>             number += 1
>             sign = -sign
>     else:
>         for number in range(2, top):
>             yield number * sign
>             sign = -sign
>
>
> def main():
>     list_ = list(gen_series(100))
>     print(list_)
>
> main()
>
>
> It's not the shortest, but it's pretty clear what's going on, and
> gen_series() is reusable.
>
>
> On Sun, Jan 4, 2015 at 3:34 AM, flebber <flebber.crue at gmail.com> wrote:
> > In repsonse to this question: Write a program that prints the first 100
> members of the sequence 2, -3, 4, -5, 6, -7, 8.
> >
> > This is my solution it works but ugly.
> >
> > series = range(2,100)
> > # answer = [(x,(y* -1)) for x, y in series[::2]]
> > # print(answer)
> > answer = []
> > for item in series:
> >     if item % 2 != 0:
> >         answer.append(item * -1)
> >     else:
> >         answer.append(item)
> >
> > print(answer)
> >
> > I know I should be better off doing this with map but cannot get it to
> work. I understand also that map returns a generator so this solution
> should only working in python2(correct me please if I am wrong).
> >
> > In [6]: map?
> > Type:       builtin_function_or_method
> > String Form:<built-in function map>
> > Namespace:  Python builtin
> > Docstring:
> > map(function, sequence[, sequence, ...]) -> list
> >
> > Just getting something wrong
> > list(map((lambda x: x * -1 if (x%2 != 0)), series))
> > --
> > https://mail.python.org/mailman/listinfo/python-list
>
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