[Tutor] Alternatives to append() for "growing" a list

[Amit Saha]

On Sun, Dec 1, 2013 at 7:27 PM, spir <denis.spir at gmail.com> wrote:
> On 12/01/2013 05:32 AM, Amit Saha wrote:
>>
>> Hello,
>>
>> I was told by someone (as a comment) that a code snippet such as this
>> "would make Pythonistas talk my ear off about how evil the append()"
>> function is:
>>
>>>>> mylist = []
>>>>> mylist.append(1)
>>
>> # a number of times over
>>
>> I have some ideas that on an append() the list's internal size
>> increases (doubled?) since CPython over-allocates memory, and such.
>>
>> So, the question is: what is the alternative to growing a list when I
>> have no idea what items or how many may be there?
>
>
> Maybe you are confusing with catenating _strings_, rather than lists.
> Python's concat is problematic because it is a binary operation. So,
> catenating n bits makes n-1 operations, each with intermediate results, of
> growing sizes, all thrown away except for the last one, the actual result.
> If all of the bitN are strings:
>         bit1 + bit2 + bit3 + bit4 + bit5
> actually constructs:
>         bit1+bit2
>         bit1+bit2+bit3
>         bit1+bit2+bit3+bit4
>         bit1+bit2+bit3+bit4+bit5
> A number of unneeded string object, and a very big useless memory weight.

Thanks Denis, good to know this is how it is done. I hadn't thought
about it simply because, never have probably concatenated strings
beyond the simple "adding a new line" to a string.


Best,
Amit.

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