Help with map python 2
tjreedy at udel.edu
Sun Jan 4 22:13:31 CET 2015
On 1/4/2015 6:34 AM, flebber 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)
for item in series:
if item % 2: # since result is a number, same as != 0
item *= -1
> 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 : map?
> Type: builtin_function_or_method
> String Form:<built-in function map>
> Namespace: Python builtin
> map(function, sequence[, sequence, ...]) -> list
> Just getting something wrong
> list(map((lambda x: x * -1 if (x%2 != 0)), series))
In py2, map produces a list already. In any case, above is syntax error
without else clause.
map(lambda x: x * -1 if x%2 else x, series)
If you do not have a function already, a list comp is better.
[(-1*k if k%2 else k) for k in range(2, N)]
Change  to () and you have a generator expression.
Terry Jan Reedy
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