[Discuss] A question for the Python gurus

[Brian Quinlan]

Adam Parkin wrote:
> Which was the original version I was complaining about. =8-p

Nope, your version had extra parens. Do you write a lot of C code that 
looks like this:

if (((((((condition))))))) {...

>> Rewrite 2
>> ---------
>>
>> for line in sys.stdin:
>>     # now do something with line
> 
> I actually tried this, but found that there were two problems:
> 
> 1) the body of the loop didn't seem to execute until after EOF was found

That is because of caching. Are you really doing interactive input or 
just testing that way?

> 2) for some reason I had to hit EOF twice to get the loop to terminate

Yeah, that's interesting and only true on Windows. The same seems to be 
true of cygwin's "cat".

> Hmm, care to elaborate why it's a "bad idea" (not efficient, confusing 
> to other programmers, etc)?  As it turns out it's also impossible, but 
> that's a side issue. =8-p

It's a bad idea because it doesn't fit with the normal practices of the 
language.

> If you're going to take 
> the functional programming approach and say "side effects are bad" then 
> you should be making deep copies of all objects passed to functions, 

This would be amazingly stupid. Since state cannot be mutated in a 
side-effect-free language, then you may as well pay by reference for 
efficiency reasons.


> Fair enough.  Now if identical strings are pooled, would that help with 
> the following example:
> 
> while 1:
>     # read a line in, string #1
>     line = sys.stdin.readline()
>     if not line:
>         break
>     
>     # remove CR from end, string #2
>     line = line.rstrip('\n')
> 
>     # Say capitalize the start of the string, string #3
>     line = line.capitalize()
> 
> Or would you have to allocate memory & copy three strings each time 
> through the loop?  

That's exactly what it will have to do.

> Now imagine if you say, want to capitalize every word in the line, then 
> the memory/time requirements would explode, would they not?  If there 
> were n words in the sentance, then you'd have to create n copies of the 
> string (or so it would seem to me -- correct me if I'm wrong).

"Explode"? The memory required will be triple the length of the line 
(plus overhead) i.e. who cares?

Cheers,
Brian