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Re: Python Interview Questions

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In article <50a911ec$0$29978$c3e8da3$5496439d@news.astraweb.com>,
 Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:

> Oh I'm sorry, did something I say suggest that the couple of examples I 
> gave are the *only* acceptable uses? My apologies for not giving an 
> exhaustive list of every possible use of lists and tuples, I'll be sure 
> to punish myself severely for the lapse.

Hmmm.  I didn't mean any offense.  I was just pointing out that what's 
true in theory and what's true in practice aren't always the same.

> Under what sort of circumstances would somebody want to take a mutable 
> list of data, say a list of email addresses, freeze it into a known 
> state, and use that frozen state as a key in a dict?

I've got a script which trolls our log files looking for python stack 
dumps.  For each dump it finds, it computes a signature (basically, a 
call sequence which led to the exception) and uses this signature as a 
dictionary key.  Here's the relevant code (abstracted slightly for 
readability):

def main(args):
    crashes = {}
    [...]
    for line in open(log_file):
        if does_not_look_like_a_stack_dump(line):
             continue
        lines = traceback_helper.unfold(line)
        header, stack = traceback_helper.extract_stack(lines)
        signature = tuple(stack)
        if signature in crashes:
            count, header = crashes[signature]
            crashes[signature] = (count + 1, header)
        else:
            crashes[signature] = (1, header)

You can find traceback_helper at 
https://bitbucket.org/roysmith/python-tools/src/4f8118d175ed/logs/traceba
ck_helper.py

The stack that's returned is a list.  It's inherently a list, per the 
classic definition:

* It's variable length.  Different stacks have different depths.

* It's homogeneous.  There's nothing particularly significant about each 
entry other than it's the next one in the stack.

* It's mutable.  I can build it up one item at a time as I discover them.

* It's ordered.  f1(f2()) is not the same as f2(f1()).

But, to use it as a dictionary key, I need to make it into a tuple, 
since keys have to be immutable.

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Re: Python Interview Questions chinjannisha@gmail.com - 2012-11-17 10:01 -0800
  Re: Python Interview Questions Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-11-18 01:54 -0500
  Re: Python Interview Questions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-18 09:39 +0000
    Re: Python Interview Questions Roy Smith <roy@panix.com> - 2012-11-18 08:53 -0500
      Re: Python Interview Questions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-18 16:50 +0000
        Re: Python Interview Questions "D'Arcy J.M. Cain" <darcy@druid.net> - 2012-11-18 12:16 -0500
        Re: Python Interview Questions Roy Smith <roy@panix.com> - 2012-11-18 12:53 -0500
          Re: Python Interview Questions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-19 00:31 +0000
            Re: Python Interview Questions Roy Smith <roy@panix.com> - 2012-11-18 21:09 -0500
              Re: Python Interview Questions Chris Angelico <rosuav@gmail.com> - 2012-11-19 13:18 +1100
              Re: Python Interview Questions Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-11-19 02:42 +0000
              Re: Python Interview Questions Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-18 23:01 -0700
              Re: Python Interview Questions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-19 07:54 +0000
                Re: Python Interview Questions Roy Smith <roy@panix.com> - 2012-11-19 09:30 -0500
                Re: Python Interview Questions Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-19 09:44 -0700
                Re: Python Interview Questions Terry Reedy <tjreedy@udel.edu> - 2012-11-19 15:41 -0500
                Re: Python Interview Questions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-19 23:42 +0000
                Re: Python Interview Questions Roy Smith <roy@panix.com> - 2012-11-19 21:33 -0500
                Re: Python Interview Questions Roy Smith <roy@panix.com> - 2012-11-19 09:59 -0500
                Re: Python Interview Questions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-19 23:53 +0000
                Re: Python Interview Questions Roy Smith <roy@panix.com> - 2012-11-19 22:14 -0500
                RE: Python Interview Questions "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-11-19 23:57 +0000
              Re: Python Interview Questions Terry Reedy <tjreedy@udel.edu> - 2012-11-19 03:27 -0500
        Re: Python Interview Questions Chris Angelico <rosuav@gmail.com> - 2012-11-19 07:02 +1100

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