Forgot to send to group. Grrr. ---------- Forwarded message ---------- From: Marc Tompkins <marc.tompk...@gmail.com> Date: Tue, Apr 19, 2011 at 10:01 AM Subject: Re: [Tutor] working with strings in python3 To: Rance Hall <ran...@gmail.com>
On Tue, Apr 19, 2011 at 6:44 AM, Rance Hall <ran...@gmail.com> wrote: > > Bottom line: Python is not BASIC. In BASIC, strings aren't immutable, > so in-place string concatenation doesn't carry (much of) a performance > > penalty. In Python, it will make your program unnecessarily slow. I > think you're under the impression that "deprecation" is a value judgment, or > that > > "message = message + foo" is deprecated because it looks like BASIC > syntax. > > Neither is true. > > Again a little misunderstanding. I didn't mean BASIC the programming > language. I forgot all I knew about that language long ago. I mean basic > in the fundamental concept sense. > No, I wasn't conflating 'basic' and BASIC, nor did I think you were - I was just using BASIC as the first example I could think of where "message = message + foo" is the standard way to concatenate strings. You can't do it that way in C or Perl or assembler; it's not recommended in Java for much the same reason as in Python ( http://www.ibm.com/developerworks/websphere/library/bestpractices/string_concatenation.html); I don't remember what I used to do in COBOL; the only example that came to mind was BASIC. Which is a different language from Python, and different rules apply, which was the only point I was trying to make. Variables are variable, that's why we call them variable. > Constants are constant, and that's why we call them constant. > > There's an old programmer's saying: "Constants aren't, and variables don't." More to the point, though, Python was designed from the ground up as an object-oriented language (as opposed to a conventional language with object support bolted on as an afterthought); both constants and variables are actually objects, and act differently than they do in a non-OO language. > We may ask ourselves "why did Guido decide to make strings immutable in > the first place?"; probably the best reason is "so that strings can be used > as keys in a dictionary", but since I'm not Guido - not even Dutch! - I > really can't speak for him. > > I'm not sure I buy this explanation as strings have been used as keys in > dictionaries or "associative arrays" for a long time, a string variable is > variable or mutable, where a keyname can not be. > Reread the two parts of your own sentence - "strings have been used as keys... for a long time" and "a string variable is variable or mutable, where a keyname can not be". It's like a Zen koan. Reconcile those two concepts and I think you will have grasped the Buddha-nature of Python strings.
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