Dharmit Shah wrote:
> I am learning Python and yesterday I cam across a definition wherein I was
> supposed to flatten a list recursively. I am getting the solution properly
> but wanted to know if I can optimize the code further.
>
> #!/usr/bin/env python
> new_list=[]
> def flatten(num_list):
> """
> >>> flatten([2, 9, [2, 1, 13, 2], 8, [2, 6]])
> [2, 9, 2, 1, 13, 2, 8, 2, 6]
> >>> flatten([[9, [7, 1, 13, 2], 8], [7, 6]])
> [9, 7, 1, 13, 2, 8, 7, 6]
> >>> flatten([[9, [7, 1, 13, 2], 8], [2, 6]])
> [9, 7, 1, 13, 2, 8, 2, 6]
> >>> flatten([[5, [5, [1, 5], 5], 5], [5, 6]])
> [5, 5, 1, 5, 5, 5, 5, 6]
> """
> global new_list
> for i in num_list:
> if type(i) == type([]):
> new_list = flatten(i)
> else:
> new_list.append(i)
> tmp = new_list
> new_list=[]
> return tmp
>
> if __name__=="__main__":
> import doctest
> doctest.testmod()
>
> PS - My knowledge of Python is still very basic and I am trying to dive into
> it as deeper as I can. Solutions on Stackoverflow.com were beyond my
> understandability.
Using doctest and getting a recursive function right don't strike me as
basic. This is pretty good for a beginner.
I'll second Peter Otten regarding the use of a global. It's best to
avoid using globals whenever possible, not just for reentrancy, but for
more readable and maintainable code. A function should be self-contained
if possible. There's no reason you can't use a local variable in this
code (and you only need one, not two), and the resulting code would be
more readable.
Regarding this line:
if type(i) == type([]):
This also works:
if type(i) == list:
But this is better:
if isinstance(i, list):
isinstance(obj, class) means "is obj an instance of class or a subtype
of class", so it's more general.
Does anyone see a way to do this with a list comprehension? I don't.
Would be a neat hack if it can be done.
--
Tom Zych / freethin...@pobox.com
"Because if they didn't vote for a lizard," said Ford, "the wrong lizard
might get in." -- DNA
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