[Tutor] filter() builtin function

[dn]

On 30/09/2021 22.22, Cameron Simpson wrote:
> On 30Sep2021 14:29, Manprit Singh <manpritsinghece at gmail.com> wrote:
>> For the filter function in Python documentation ,  a line is written as
>> below:
>>
>> Construct an iterator from those elements of *iterable* for which *function*
>> returns true.
>>
>> *What does that true means - Boolen  value True or true object - for
>> example 1*
> 
> A true object will do.
> 
>> *Like if I need only odd numbers from a list , what will be the correct
>> lambda function to be placed inside the filter function ?*
> 
> A test that a number is odd:
> 
>     lambda n: test-if-n-is-odd
> 
>> *lambda x: x%2  (That will return 1  for odd numbers which is a true
>> object)*
> 
> That would do. I would probably be inclined to go the whole way:
> 
>     lambda x: x%2 == 1
> 
> to make my meaning clear.
> 
>> *lambda x : x%2 == 1 ( Will return Boolean True for odd  numbers)*
> 
> I'd do that, but only for purposes of clarity.
> 
>> seq = [2, 3, 6, 9, 0, 7]
>> list(filter(lambda x: x%2, seq))
>> gives the answer
>> = [3, 9, 7]
> 
> Seems correct.
> 
>> seq = [2, 3, 6, 9, 0, 7]
>> list(filter(lambda x: x%2 == 1, seq))  also gives the same answer = [3, 9, 7]
>>
>> Which one is the correct  way to do the task solved  just above  in 2 
>> ways ?
> 
> They're both correct. The second one more precisely specifies "oddness".
> 
> You seem heavily invested in "correct" and 'acceptable" ways to do 
> things. For many of us, there are good ways and bad ways to do things, 
> but things are only "incorrect" if they will give wrong answers i.e.  
> they are buggy.
> 
> As usual my generic advice is:
> - concise
> - readable


+1
Surely though, are themselves arguments against using an (unnamed)
lambda function, instead of:

def is_odd( number ):
    return number % 2 == 1

leading to:

list( filter( is_odd, seq) )

instead of:

list(filter(lambda x: x%2, seq))

Zen: explicit > implicit


If valuing "concise" and "clever", consider employing
list-comprehensions/generators.
-- 
Regards,
=dn