On 2006-09-22, sam <[EMAIL PROTECTED]> wrote:
> i am starting to experiment with recursion, and decided to
> write a fairly trivial little program which took a float as
> input, then called a function to halve it recursively until it
> was less than 1:
>
> ____________________________________________________________________
> import recursive_halve_module
>
> raw_value = raw_input('please enter the number you would like to halve:
> ')
> value = float(raw_value)
>
> final_value = recursive_halve_module.recursive_halve(value)
>
> print final_value
>
> raw_input('hit enter to close: ')
> _____________________________________________________________________
>
> def recursive_halve(value):
>
> if value < 1:
> print value
> return value
> else:
> value = value/2
> print value
> if value < 1:
> return value
> else:
> recursive_halve(value)
Your immediate bug is that you're missing a return statement:
return recursive_halve(value)
But your recursive routine is overcomplicated with too many base
cases, and you haven't written it functionally. There's no need
to modify value directly in a functional procedure.
Here's another version.
def recursive_halve(value):
if value < 1.0:
return value
else:
return recursive_halve(value / 2.0)
Now imagine the call-stack when called with value 45.0 (using the
substitution model):
recursive_halve(45.0) -->
return recursive_halve(22.5) -->
return recursive_halve(11.25) -->
return recursive_halve(5.625) -->
return recursive_halve(2.8125) -->
return recursive_halve(1.40625) -->
return recursive_halve(0.703125) -->
return 0.703125
--
Neil Cerutti
Life is indeed precious, and I believe the death penalty helps
affirm this fact. --Edward Koch
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