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Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?

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From Tim Chase <python.list@tim.thechases.com>
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Subject Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?
Date Sun, 8 May 2016 18:37:38 -0500
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While I'm not Steven...

On 2016-05-08 19:10, DFS wrote:
> sSQL =  "line 1\n"
> sSQL += "line 2\n"
> sSQL += "line 3"

If you're only doing it once, it's adequate.

If you're doing it within a loop

  for thing in some_iter():
    s = "line1\n"
    s += "line2\n"
    s += "line3"
    use(s, thing)

it's suboptimal.  Solutions include hoisting it out of the loop:

  s = "line1\n"
  s += "line2\n"
  s += "line3"
  for thing in some_iter():
    use(s, thing)

and just specifying it with a multi-line string (still better off
hoisted out of the loop):

  s = """line1
line2
line3"""
  for thing in some_iter():
    use(s, thing)

If you're accruing in a loop

  s = ""
  for thing in some_iter():
    s += mung(thing)

then that's a bad code-smell (you get quadratic behavior as the
strings are constantly resized), usually better replaced with

  s = "".join(mung(thing) for thing in some_iter())

or build them up as a list, then join the results:

  lst = []
  for thing in some_iter():
    if should_use(thing):
      lst.append(thing)
  s = "\n".join(lst)

-tkc

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Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-08 19:10 -0400
  Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Tim Chase <python.list@tim.thechases.com> - 2016-05-08 18:37 -0500
  Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Joel Goldstick <joel.goldstick@gmail.com> - 2016-05-08 20:02 -0400
  String concatenation (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-05-09 02:44 +0200
    Re: String concatenation (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) Chris Angelico <rosuav@gmail.com> - 2016-05-09 12:16 +1000
      Re: String concatenation Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-05-09 23:21 +0200
        Re: String concatenation Steven D'Aprano <steve@pearwood.info> - 2016-05-10 12:32 +1000
          Re: String concatenation Chris Angelico <rosuav@gmail.com> - 2016-05-10 12:42 +1000
            Re: String concatenation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-05-12 17:43 +1000
        Re: String concatenation Rustom Mody <rustompmody@gmail.com> - 2016-05-09 20:45 -0700
          Re: String concatenation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-05-10 16:46 +1000
            Re: String concatenation Paul Rubin <no.email@nospam.invalid> - 2016-05-10 00:13 -0700
              Re: String concatenation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-05-10 17:54 +1000
                Re: String concatenation David Palao <dpalao.python@gmail.com> - 2016-05-10 10:15 +0200
                Re: String concatenation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-05-12 17:27 +1000
    Re: String concatenation (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) srinivas devaki <mr.eightnoteight@gmail.com> - 2016-05-09 09:01 +0530
    Re: String concatenation (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) srinivas devaki <mr.eightnoteight@gmail.com> - 2016-05-09 09:13 +0530
    Re: String concatenation (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) Michael Selik <michael.selik@gmail.com> - 2016-05-09 18:29 +0000
    Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 19:53 -0400
      Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-05-11 02:16 +0200
        Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 20:33 -0400
        Moderation [was Re: ...What's wrong with this concatenation statement?] Steven D'Aprano <steve@pearwood.info> - 2016-05-11 11:17 +1000
        Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Chris Angelico <rosuav@gmail.com> - 2016-05-11 11:43 +1000
          Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-05-11 21:12 +0200
        Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Ned Batchelder <ned@nedbatchelder.com> - 2016-05-11 12:39 -0700
          Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Chris Angelico <rosuav@gmail.com> - 2016-05-12 09:07 +1000
          Re: % formatting vs .format() (was: What's wrong with this concatenation statement?) Tim Chase <python.list@tim.thechases.com> - 2016-05-11 18:31 -0500
    Re: String concatenation (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) sohcahtoa82@gmail.com - 2016-05-10 17:38 -0700
      Re: String concatenation Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-05-11 21:14 +0200
        Re: String concatenation sohcahtoa82@gmail.com - 2016-05-11 14:30 -0700
          Re: String concatenation Ned Batchelder <ned@nedbatchelder.com> - 2016-05-11 14:50 -0700
          Re: String concatenation DFS <nospam@dfs.com> - 2016-05-11 18:25 -0400
  Re: What's wrong with this concatenation statement? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-05-09 17:53 +1000
    Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 12:16 -0400
      Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Rustom Mody <rustompmody@gmail.com> - 2016-05-10 09:41 -0700
      Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Stephen Hansen <me+python@ixokai.io> - 2016-05-10 09:42 -0700
        Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 18:37 -0400
      Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Steven D'Aprano <steve@pearwood.info> - 2016-05-11 02:44 +1000
      Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Ian Kelly <ian.g.kelly@gmail.com> - 2016-05-10 12:15 -0600
        Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 17:21 -0400
          Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Chris Angelico <rosuav@gmail.com> - 2016-05-11 07:27 +1000
            Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 19:40 -0400
              Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Paul Rubin <no.email@nospam.invalid> - 2016-05-10 19:14 -0700
              Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? alister <alister.ware@ntlworld.com> - 2016-05-12 09:12 +0000
                Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Chris Angelico <rosuav@gmail.com> - 2016-05-12 19:23 +1000
                Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-12 08:24 -0400
                Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Michael Torrie <torriem@gmail.com> - 2016-05-12 08:39 -0600
                Why online forums have bad behaviour (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) Ben Finney <ben+python@benfinney.id.au> - 2016-05-13 05:36 +1000
                Re: Why online forums have bad behaviour (was: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement?) Jason Friedman <jsf80238@gmail.com> - 2016-05-12 21:05 -0600
          Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Ethan Furman <ethan@stoneleaf.us> - 2016-05-10 15:12 -0700
            Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 19:29 -0400
              Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-05-12 13:39 +0000
                Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Chris Angelico <rosuav@gmail.com> - 2016-05-12 23:50 +1000
          Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Ethan Furman <ethan@stoneleaf.us> - 2016-05-10 16:16 -0700
            Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? DFS <nospam@dfs.com> - 2016-05-10 19:41 -0400
  Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? srinivas devaki <mr.eightnoteight@gmail.com> - 2016-05-12 13:53 +0530
    Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Ned Batchelder <ned@nedbatchelder.com> - 2016-05-12 02:36 -0700
      Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Steven D'Aprano <steve@pearwood.info> - 2016-05-13 01:06 +1000
  Re: Steve D'Aprano, you're the "master". What's wrong with this concatenation statement? Chris Angelico <rosuav@gmail.com> - 2016-05-12 18:40 +1000

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