On 9/28/2011 5:28 AM, Xah Lee wrote:
curious question.
suppose you have 300 different strings and they need all be replaced
to say "aaa".
is it faster to replace each one sequentially (i.e. replace first
string to aaa, then do the 2nd, 3rd,...)
, or is it faster to use a regex with “or” them all and do replace one
shot? (i.e. "1ststr|2ndstr|3rdstr|..." -> aaa)
Here the problem is replace multiple random substrings with one random
substring that could create new matches. I would start with the re 'or'
solution.
btw, the origin of this question is about writing a emacs lisp
function that replace ~250 html named entities to unicode char.
As you noted this is a different problem in that there is a different
replacement for each. Also, the substrings being searched for are not
random but have a distinct and easily recognized structure. The
replacement cannot create a new match. So the multiple scan approach
*could* work.
Unspecified is whether the input is unicode or ascii bytes. If the
latter I might copy to a bytearray (mutable), scan forward, replace
entity defs with utf-8 encoding of the corresponding unicode (with a
dict lookup, and which I assume are *always* fewer chars), and shift
other chars to close any gaps created.
If the input is unicode, I might do the same with array.array (which is
where bytearray came from). Or I might use the standard idiom of
constructing a list of pieces of the original, with replacements, and
''.join() at the end.
--
Terry Jan Reedy
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