[Tutor] Replace a character by index

[Kent Johnson]

On Thu, Jul 16, 2009 at 4:29 AM, Wayne<srilyk at gmail.com> wrote:
> Hi,
>
> My question is more about style/timing than anything else.
>
> In my program I'm taking a word and generating "blanks" in that word. For
> example, the word cat could generate:
> _at
> c_t
> ca_
>
> I have two different ways I can put _ in the word:
> word = 'cat'
>
> ''.join(list(word)[1] = '_')

Not in any Python I ever used...
In [1]: word = 'cat'

In [2]:

In [3]: ''.join(list(word)[1] = '_')
------------------------------------------------------------
   File "<ipython console>", line 1
SyntaxError: keyword can't be an expression (<ipython console>, line 1)

>
> and
>
> # I'm not using a constant, but randomly generating where the blank appears
> word[:1] + '_' + word[1+1:]
>
> So, when I use the timeit module I get these results:
>
> In [78]: timeit.Timer("''.join(list('foo'))").timeit()
> Out[78]: 2.9940109252929688
>
> In [80]: timeit.Timer("'foo'[:2]+'_'+'foo'[2+1:]").timeit()
> Out[80]: 0.63733291625976562
>
> Quite a significant difference.
>
> So my question(s): Which method should I use/is more pythonic? Which method
> do you/have you used? And the ubiquitous 'Why?'

Um, the second method is faster and has the advantage of working :-)
Seems like a no-brainer to me!

Kent