On Fri, 20 Apr 2007 15:21:56 -0700, John Machin wrote:
> On Apr 20, 9:12 am, Steven D'Aprano
> <[EMAIL PROTECTED]> wrote:
>> On Thu, 19 Apr 2007 13:57:16 -0700, Boris Dusek wrote:
>> >> > what is the use-case of parameter "start" in string's "endswith"
>> >> > method?
>>
>> >> def foo(function,instance,param):
>> >> if function(instance,param,2,4):
>> >> return True
>> >> else: return False
>>
>> >> The function must work whether you pass it
>> >> foo(str.endswith,"blaahh","ahh"), or
>> >> foo(str.startswith,"blaahh","aah"). This is a really bad example, but
>> >> it gets the point across that similar functions must have similar
>> >> parameters in order to be Pythonic.
>>
>> > Thanks for explanation, this point makes sense. And I agree that I can
>> > hardly imagine any use of both parameters :-).
>>
>> No, sorry, it doesn't make sense because not all string methods take the
>> same arguments! See, for instance, ''.translate() and ''.lower().
>>
>> The best reason for giving string methods and functions start and end
>> parameters is to avoid copying potentially large lumps of text. Here's a
>> silly example. Instead of doing this:
>>
>> while text:
>> p = text.find('parrot')
>> buffer = text[:p]
>> text = text[p:]
>> do_something_with(buffer)
>>
>> You can do this:
>>
>> p = 0
>> while text:
>> p = text.find('parrot', p)
>> do_something_with(buffer, p)
>>
>> which avoids copying text unnecessarily.
>
> ... but increases the care and attention required when coding:
There are always trade-offs.
>
> (1) "while text"? "while 1" is a more obvious way of stress-testing
> your CPU fan :-) but perhaps you meant "while p >= 0".
No, I meant exactly what I said. You might notice that text becomes
smaller after each iteration:
text = text[p:]
Eventually text becomes the empty string and the while loop is exited
cleanly.
"while p >= 0" would be an alternative, but you still need to copy chars
into a buffer, and you still need to shrink the text or else you'll just
keep getting the same p over and over again.
> (2) 4s/buffer/text/
Yes, a silly typo caused by copy-and-paste-without-proof-reading.
--
Steven.
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