[Tutor] working with strings in python3

Mon Apr 18 22:16:52 EDT 2011

On 2011年4月19日 10:34:27 +1000, James Mills wrote:
> Normally it's considered bad practise to concatenate strings. 

*Repeatedly*.
There's nothing wrong with concatenating (say) two or three strings. 
What's a bad idea is something like:
s = ''
while condition:
 s += "append stuff to end"
Even worse:
s = ''
while condition:
 s = "insert stuff at beginning" + s
because that defeats the runtime optimization (CPython only!) that 
*sometimes* can alleviate the badness of repeated string concatenation.
See Joel on Software for more:
http://www.joelonsoftware.com/articles/fog0000000319.html
But a single concatenation is more or less equally efficient as string 
formatting operations (and probably more efficient, because you don't 
have the overheard of parsing the format mini-language).
For repeated concatenation, the usual idiom is to collect all the 
substrings in a list, then join them all at once at the end:
pieces = []
while condition:
 pieces.append('append stuff at end')
s = ''.join(pieces)
-- 
Steven