Help with map python 2

Sun Jan 4 13:06:06 EST 2015

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))
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