[BangPypers] Python List Comprehension Question

[kracekumar ramaraju]

On Fri, Oct 3, 2014 at 9:04 PM, Bhargav Kowshik <
bhargav.kowshik at yahoo.com.dmarc.invalid> wrote:

> Nice! Thank you very much Anand.But, I still don't know what is
> happening.Please point me to a resource to understand what is happening.
>
>
A common beginner mistake. More of such gotcha can be found here
http://docs.python-guide.org/en/latest/writing/gotchas/ .



> ** Program **
>
> def flat_it(values, result=list()):
>     for v in values:
>         if isinstance(v, list):
>             flat_it(v, result)
>         else:
>             result.append(v)
>     return result
>
> x = [[1, 2, [3, 7]], 4]
>
> print('Input: {0}'.format(x))
> print('Output 1: {0}'.format(flat_it(x)))
> print('Output 2: {0}'.format(flat_it(x)))
> print('Output 3: {0}'.format(flat_it(x, list())))
>
> ** Output **
> Input: [[1, 2, [3, 7]], 4]
> Output 1: [1, 2, 3, 7, 4]
> Output 2: [1, 2, 3, 7, 4, 1, 2, 3, 7, 4]
> Output 3: [1, 2, 3, 7, 4]
>
> Thank you,
> Bhargav.
>
>
>      On Friday, October 3, 2014 8:48 PM, Anand Chitipothu <
> anandology at gmail.com> wrote:
>
>
>
>  On Fri, Oct 3, 2014 at 8:26 PM, Bhargav Kowshik
> <bhargav.kowshik at yahoo.com.dmarc.invalid> wrote:
>
> We could use what Anand talked about at Pycon India about handling the
> headers in first row of a CSV.In this scenario, instead of default for
> result being None and checking if None everytime, we could have the default
> value an empty list.
>
> def flat_it(values, result=list()):
>     for v in values:
>         if isinstance(v, list):
>             flat_it(v, result)
>         else:
>             result.append(v)
>     return result
>
> x = [[1, 2, [3, 4, 5, 6, 7]], 4]
> print x
> print flat_it(x)
>
>
> Thats a pitfall! Try calling flat_it once again and see what you get.
> Anand
>
>
>
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