more efficient?

[Zubin Mithra]

thank you for your help and support. i`ll keep your advice in mind. :)

cheers!!!
Zubin



On Tue, Dec 22, 2009 at 8:07 PM, Lie Ryan <lie.1296 at gmail.com> wrote:
> On 12/22/2009 5:13 PM, Zubin Mithra wrote:
>>
>> I have the following two implementation techniques in mind.
>>
>> def myfunc(mystring):
>>     check = "hello, there " + mystring + "!!!"
>>     print check
>>
>>
>> OR
>> structure = ["hello, there",,"!!!"]
>> def myfunc(mystring):
>>     structure[2] = mystring
>>     output = ''.join(mystring)
>>
>> i heard that string concatenation is very slow in python; so should i
>> go for the second approach? could someone tell me why? Would there be
>> another 'best-practice-style'?
>> Please help. Thankx in advance!
>
> Python's strings are immutable and to concatenate two string the interpreter
> need to copy two whole string into a new string object. This isn't a
> performance problem until you're trying to concatenate a list containing a
> thousand strings:
> ['abc', 'bcd', 'cde', 'def', ...]
> with the naive approach:
> joined = ''
> for s in lst:
>    joined = joined + s
>
> first python will conc. '' and 'abc', copying 0+3 = 3 chars
> then it conc. 'abc' and 'bcd', copying 3+3 = 6 chars
> then it conc. 'abcbcd' and 'cde' copying 6+3 = 9 chars
> then it conc. 'abcbcdcde' and 'def' copying 9+3 = 12 chars
> and so on...
>
> for four 3-letter strings, python copies 3 + 6 + 9 + 12 = 30 chars, instead
> of the minimum necessary 12 chars. It gets worse as the number of strings
> increases.
>
> When you concatenate two 1000-chars large strings, both + and ''.join will
> have to copy 2000 chars. But when you join one thousand 2-chars string
> you'll need to copy 1001000 chars[!] with +.
>
> Now, early optimization *is evil*. Don't start throwing ''.join every here
> and there. The performance by the concatenations won't start to matter until
> you're concatenating a large lists (>40) and + is much more readable than
> ''.join().
>
> When concatenating small number of strings I preferred
> %-interpolation/str.format; it's often much more readable than ''.join and
> +.
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>