[Tutor] String concatenation too slow

[wesley chun]

> I've been
>  using string concatenation to read through the string, and then create
>  the new one based on a dictionary lookup. However it becomes very slow
>  once the string gets very long (several thousand characters). [...]
> I was wondering if there might be a
>  faster alternative to string concatenation. Would appending to a list
>  of strings be faster?

without knowing more about your application, my 1st inclination would
be to turn your code that "appends" each successive addition to the
string into a generator function.  then when you need to final
massively large string, i'd use a generator expression inside the call
to the delimiter's join() method.

for example:

def nextLsystem(...):
        :
    for n in range(XXX):
        # blah-blah stuff in a loop
        yield nextStr

final = ''.join(x for x in nextLsystem(XXX))

i like this code because it doesn't keep building up a data structure
like continuously concatenating strings nor continually appending to a
list, both of which are memory-intensive.

i'm using a generator to create each successive string, without saving
previous result necessarily.  then the generator expression -- unlike
a list comprehension which must build an entire list -- passes each
string to join(), which then creates the final string.

i'm sure others have better ideas, but like it said, it's just a gut
shot from me here.

good luck!
-- wesley
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"Core Python Programming", Prentice Hall, (c)2007,2001
    http://corepython.com

wesley.j.chun :: wescpy-at-gmail.com
python training and technical consulting
cyberweb.consulting : silicon valley, ca
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