[Tutor] longest common substring

[lina]

On Sun, Nov 13, 2011 at 12:40 AM, Andreas Perstinger
<andreas.perstinger at gmx.net> wrote:
> On 2011-11-12 16:24, lina wrote:
>>
>> Thanks, ^_^, now better.
>
> No, I'm afraid you are still not understanding.
>
>> I checked, the sublist (list) here can't be as a key of the results
>> (dict).
>
> "result" isn't a dictionary. It started as an empty list and later becomes a
> null object ("NoneType").
>
> You must not forget that you are inside a for-loop. Simplified your
> situation is like this:
>
>>>> result = []
>>>> for i in range(1,10):
> ...     print("Iteration {0}, result = {1}".format(i, result))
> ...     result = result.append(i)
> ...
> Iteration 1, result = []
> Iteration 2, result = None
> Traceback (most recent call last):
>  File "<stdin>", line 3, in <module>
> AttributeError: 'NoneType' object has no attribute 'append'
>
> As you see the error happens in the *second* iteration, because result is no
> list any more.
> Dave gave you already the explanation: functions and method always return a
> value in Python. If the don't have a return statement they return "None".
>
> Another simple example:
>
>>>> a = print("Test")
> Test
>
> "print" is a function which prints out the text you passed to it and you
> usually aren't interested in its return value. But every function/method in
> Python returns something. You save this value in "a"
>
>>>> print(a)
> None
>
> As you see the return value of "print" is "None".
>
>>>> a.append(x)
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> AttributeError: 'NoneType' object has no attribute 'append'
>
> Same error as above, because "NoneType" objects (null objects) don't have a
> method "append".
>
> I also think you mix two different ways to add an element to a list:
>
> result.append(x)
>
> is equivalent to
>
> result = result + [x] (that's what you will use in other languages)

Finally, if I am not wrong again, I feel I am kinda of starting
figuring out what's going on. Why it's None.

The main mistake here I use result = result.append(something)
the "="

I checked the print(id(result)) and print(id(result.append()),

For the NoneType they shared the same id 8823392 in my laptop. is it
temporary address?

>
> HTH, Andreas

Really helps, Thanks again.

 haha ...for the emails from the list I used to read several times,
again and again to understand.

Best regards,

> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> To unsubscribe or change subscription options:
> http://mail.python.org/mailman/listinfo/tutor
>