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About a list comprehension to transform an input list

Emile van Sebille emile at fenx.com
Fri Jun 8 12:43:55 EDT 2012 
On 6/8/2012 9:17 AM Daniel Urban said...
> On Fri, Jun 8, 2012 at 6:10 PM, Julio Sergio<juliosergio at gmail.com>  wrote:
>> > From a sequence of numbers, I'm trying to get a list that does something to even
>> numbers but leaves untouched the odd ones, say:
>>
>> [0,1,2,3,4,...] ==>  [100,1,102,3,104,...]
>>
>> I know that this can be done with an auxiliary function, as follows:
>>
>> ->>>  def filter(n):
>> ...     if (n%2 == 0):
>> ...         return 100+n
>> ...     return n
>> ...
>> ->>>  L = range(10)
>> ->>>  [filter(n) for n in L]
>> [100, 1, 102, 3, 104, 5, 106, 7, 108, 9]
>>
>> I wonder whether there can be a single list comprehension expression to get this
>> result without the aid of the auxiliary function.
>>
>> Do you have any comments on this?
>
>>>> l = [0,1,2,3,4,5,6,7,8,9]
>>>> [n if n%2 else 100+n for n in l]
> [100, 1, 102, 3, 104, 5, 106, 7, 108, 9]
>

Or alternately by leveraging true/false as 1/0:

 >>> [ 100*(not(ii%2))+ii for ii in range(10)]
[100, 1, 102, 3, 104, 5, 106, 7, 108, 9]
 >>> [ 100*(ii%2)+ii for ii in range(10)]
[0, 101, 2, 103, 4, 105, 6, 107, 8, 109]
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