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Date: Sat, 15 Jun 2024 00:45:24 -0400
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Subject: Re: "undefined behavior"?
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On 6/14/2024 11:56 PM, Keith Thompson wrote:
> DFS <nospam@dfs.com> writes:
>> On 6/14/2024 9:39 PM, Keith Thompson wrote:
>>> DFS <nospam@dfs.com> writes:
>>> [...]
>>>> During conversion, I got a Python error I don't remember seeing in the past:
>>>>
>>>> "TypeError: list indices must be integers or slices, not float"
>>>>
>>>> because division returns a float, and some of the array addressing was
>>>> like this: nums[i/2].
>>> [...]
>>> C's "/" operator yields a result with the type of the operands
>>> (after
>>> promotion to a common type).
>>> Python's "/" operator yields a floating-point result.  For C-style
>>> integer division, Python uses "//".  (Python 2 is more C-like.)
>>
>> I was surprised python did that, since every division used in the
>> array addressing results in an integer.
>>
>> After casting i to an int before any array addressing, // works.
> 
> I'm surprised you needed to convert i to an int.  I would think that
 > just replacing nums[i/2] by nums[i//2] would do the trick,
 > as long> as i always has an int value (note Python's dynamic typing). 
  If i
> is acquiring a float value, that's probably a bug, given the name.

I spotted the issue.  Just prior to using i for array addressing I said:
i = N/2.

The fix is set i = int(N/2)



> But if you want help with your Python code, comp.lang.python is the
> place to ask.

Thanks for your help, but David Brown is a Python developer and I'll ask 
him python questions here whenever I care to.

In the recent past you were involved in discussions on perl, Fortran and 
awk, among other off-topics.

Rules for thee but not for me?