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Re: Tuple of lists concatenation - function vs comprehension

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  Re: Tuple of lists concatenation  -  function vs comprehension Terry Reedy <tjreedy@udel.edu> - 2014-12-07 17:21 -0500
    Re: Tuple of lists concatenation  -  function vs comprehension Rustom Mody <rustompmody@gmail.com> - 2014-12-09 06:16 -0800

#82078 — Re: Tuple of lists concatenation - function vs comprehension

On 12/7/2014 10:28 AM, Ivan Evstegneev wrote:
> Hi Shiyao,
>
> Now I see, that it was kind of dumb question...
>
>>>>> x = ([1, 2], [3, 4], [5, 6])
>>>>> L = []
>>>> [L.extend(i) for i in x]
> [None, None, None]

Using a list comprehension for the expression side-effect, when you do 
not actually want the list produced by the comprehension, is considered 
bad style by many.  There is nothing wrong with explicit loops.

> BUT when I check L itself I'll see this one
>
>>>> L
> [1,2,3,5,6]


-- 
Terry Jan Reedy

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#82199

On Monday, December 8, 2014 3:52:53 AM UTC+5:30, Terry Reedy wrote:
> On 12/7/2014 10:28 AM, Ivan Evstegneev wrote:
> > Hi Shiyao,
> >
> > Now I see, that it was kind of dumb question...
> >
> >>>>> x = ([1, 2], [3, 4], [5, 6])
> >>>>> L = []
> >>>> [L.extend(i) for i in x]
> > [None, None, None]
> 
> Using a list comprehension for the expression side-effect, when you do 
> not actually want the list produced by the comprehension, is considered 
> bad style by many.  There is nothing wrong with explicit loops.

Yes loops are ok

If you want a solution along the lines you (OP) are seeking here is one:

>>> from operator import add
>>> reduce(add,  [[1,2],[3,4]],  [])
[1, 2, 3, 4]
>>> 

Notes
1. Terry's suggestion to use (the obvious) loop should be heeded
2. Which will also be more efficient
3. The reason I mention the reduce is that its a part of FP lore:
Every map (and therefore comprehension) can be put into the form of a reduce.
But not the contrary.

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