[Tutor] Are you allowed to shoot camels? [kinda OT]

Jeff Shannon jeff at ccvcorp.com
Tue Feb 8 21:41:26 CET 2005

Smith, Jeff wrote:

> Jeff,
> It looks like that finally is the simplest expression of the original
> switch statement:
> import sys
> def p():
>     pass
> ftable = { 'a' : lambda: sys.stdout.write('a\n'),
>            'b' : lambda: sys.stdout.write('b or c\n'),
>            'c' : lambda: sys.stdout.write('b or c\n'),
>            'd' : p }
> ftable.get(var, lambda: sys.stdout.write('default case\n'))()
> I do note that it took this group of experienced programmers several
> tries to impliment this simple switch statement without actually using
> switch.  I dare say with standard switch syntax we would've had it right
> the first time :-)

I wasn't following this thread all the way through, but to be honest,
I'd have solved this differently -- that may be the best "direct
translation" of some switch statement, but that doesn't mean it's the
best-fit solution here.  ISTM that, given the desire to print some
text (or nothing) based on the contents of a variable, I would *not*
handle the output inside the "switch" -- that is, I'd (conditionally)
print a value from a string-containing dictionary, rather than use a
table of functions that print strings.

table = { 'a': 'a', 'b': 'b or c', 'c': 'b or c', 'd': None }
result = table.get(var, 'default case')
if result:
     print result

This, to my mind, is much cleaner -- you're factoring out the repeated
code, whether print statement or call to sys.stdout.write(), reducing
the complexity of the dict.  You're making flow control much more
straightforward.  You're making the whole thing easier to read.

The key, here, is that instead of saying "I want a switch, how can I
implement that in Python?", I've taken the approach of "The end result
I want is ***; what tools does Python offer to achieve that?"  This
conceptual shift is, IMHO, *the* most important mental hurdle in
learning a [second/third/n-th] language.

Jeff Shannon
Credit International

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