Easy function, please help.

Benjamin Kaplan benjamin.kaplan at case.edu
Thu Feb 10 09:31:41 CET 2011


On Thu, Feb 10, 2011 at 12:03 AM, Jason Swails <jason.swails at gmail.com> wrote:
>
>
> On Wed, Feb 9, 2011 at 5:34 PM, MRAB <python at mrabarnett.plus.com> wrote:
>>
>> On 09/02/2011 21:42, Jason Swails wrote:
>>>
>>> You've gotten several good explanations, mainly saying that 0 -> False
>>> and not 0 -> True, which is why the while loop exits.  You've also
>>> gotten advice about how to make your method more robust (i.e. force
>>> integer division).
>>>
>>> However, as surprising as this may be I'm actually with RR on this one
>>> (for a little) -- for code readability's sake, you should make your
>>> conditional more readable (i.e. don't depend on the fact that the
>>> iterations will take your test value down to 0 which conveniently in
>>> this case evaluates to False).  This could encourage you in later cases
>>> to think that if this result eventually converged to a different number,
>>> say the multiplicative identity instead, that the same approach will
>>> work (when instead it'll dump you into an infinite loop).
>>>
>>> You've also gotten the suggestion of typecasting to a string and then
>>> looking at the number of characters in the string.  This works fine for
>>> integers and positive numbers, but not so well for negatives and floats,
>>> since both the decimal and negative sign will be counted.  You could
>>> typecast to a string then strip out '-' and '.' and then count the
>>> characters.  i.e.
>>>
>>> def num_digits(n):
>>>    return len(str(n).replace('-','').replace('.',''))
>>>
>> Or:
>>
>> def num_digits(n):
>>    return len(str(abs(n)).replace('.',''))
>>
>>> Or typecast to an int if you want to neglect decimals before converting
>>> to a string, etc.
>>>
>> [snip]
>> Python doesn't have typecasting. :-)
>
> Because these basic types are not mutable?  <excuse> Most of my work has to
> be in Fortran, so I'm a relative newcomer to Python.  When I don't need
> Fortran-y performance it's much nicer (obviously to anyone that's used them
> both)!  Still don't know much deeper than Python's cosmetic surface at this
> point. </excuse>
>

Not exactly. It's because everything in Python is an object. What
you're doing isn't type casting. It's just calling an object
constructor- no different than any other class in the language.



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