Can you make this faster?

[Ype Kingma]

alejandro david weil wrote:

> On Sun June 27 2004 15:22, Kamilche wrote:
>> I have a routine that I really need, but it slows down processing
>> significantly. Can you spot any ineffeciencies in the code?
>>
>> This code makes a critical function of mine run about 7x slower than
>> using a prebuilt format string. For maximum flexibility, it would be
>> best to calculate the format string using this method, so I'd dearly
>> love to keep it.
>>
...

> 
> But, anyway, the problem seems to be the:
>       f2 += str(len(arg))
> line.

You can try this (untested):

def myfmtstring(args):
        global typedic
        f2l = ['<']
        t = None
        for arg in args:
                t = type(arg)
                if t == types.StringType:
                        f2l.append(str(len(arg)))
                try:
                        f2l.append(typedic[t])
                except: #check the exception here!
                        raise Exception("Can't pack argument of type %s!" % t)
        fl2.append('\0')
        return ''.join(f2l)

> If you take it off, you'll see that time reduces to half!
> Why? How to fix?

Appending to a string copies the original completely.

Good luck,
Ype


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